diff --git a/src/dotnet-svcutil/lib/src/CodeDomFixup/VisitorFixup.cs b/src/dotnet-svcutil/lib/src/CodeDomFixup/VisitorFixup.cs
index c1cf8550dd8..080f8856564 100644
--- a/src/dotnet-svcutil/lib/src/CodeDomFixup/VisitorFixup.cs
+++ b/src/dotnet-svcutil/lib/src/CodeDomFixup/VisitorFixup.cs
@@ -12,7 +12,11 @@ internal class VisitorFixup : CodeFixup
     {
         private static CodeDomVisitor[] GetVisitors(ServiceContractGenerator generator, CommandProcessorOptions options)
         {
-            ArrayOfXElementTypeHelper arrayOfXElementTypeHelper = new ArrayOfXElementTypeHelper((generator.Options & ServiceContractGenerationOptions.InternalTypes) == ServiceContractGenerationOptions.InternalTypes, generator.TargetCompileUnit);
+            // Keep the ArrayOfXElement helper public even under --internal.
+            // WCF's XmlSerializer operation behavior generates serializer assemblies at runtime; those assemblies cannot
+            // reference internal types, so internal schema/message types can fail at runtime. Keeping this helper public
+            // avoids inconsistent accessibility without breaking XmlSerializer runtime behavior.
+            ArrayOfXElementTypeHelper arrayOfXElementTypeHelper = new ArrayOfXElementTypeHelper(isInternal: false, generator.TargetCompileUnit);
             bool isVisualBasic = IsVisualBasicLanguage(options?.Language);
 
             CodeDomVisitor[] visitors = new CodeDomVisitor[]
diff --git a/src/dotnet-svcutil/lib/src/ImportModule.cs b/src/dotnet-svcutil/lib/src/ImportModule.cs
index eb517fdda18..9d16b29dcb1 100644
--- a/src/dotnet-svcutil/lib/src/ImportModule.cs
+++ b/src/dotnet-svcutil/lib/src/ImportModule.cs
@@ -16,6 +16,7 @@
 using System.Linq;
 using System.ServiceModel.Channels;
 using System.ServiceModel.Description;
+using System.Threading;
 
 using DcNS = System.Runtime.Serialization;
 using WsdlNS = System.Web.Services.Description;
@@ -24,6 +25,8 @@ namespace Microsoft.Tools.ServiceModel.Svcutil
 {
     internal partial class ImportModule
     {
+        private static int s_internalWithXmlSerializerWarningEmitted;
+
         private readonly CodeCompileUnit _codeCompileUnit;
         private readonly WsdlImporter _wsdlImporter;
         private readonly ServiceContractGenerator _contractGenerator;
@@ -125,6 +128,11 @@ public bool AfterImportMetadata(ServiceDescriptor serviceDescriptor)
         {
             try
             {
+                if (_options.InternalTypeAccess == true && UsesXmlSerializer(serviceDescriptor, _options))
+                {
+                    EmitInternalWithXmlSerializerWarningOnce();
+                }
+
                 // Convert errors to warnings to workaround the issue that many validation errors from XSD compiler
                 // can be ignored.
                 for (int idx = _wsdlImporter.Errors.Count - 1; idx >= _nonWsdlImportErrors; idx--)
@@ -176,6 +184,46 @@ public bool AfterImportMetadata(ServiceDescriptor serviceDescriptor)
             return contractsResolved;
         }
 
+        private static bool UsesXmlSerializer(ServiceDescriptor serviceDescriptor, CommandProcessorOptions options)
+        {
+            if (options?.SerializerMode == SerializerMode.XmlSerializer)
+            {
+                return true;
+            }
+
+            if (serviceDescriptor?.Contracts == null)
+            {
+                return false;
+            }
+
+            foreach (ContractDescription contract in serviceDescriptor.Contracts)
+            {
+                if (contract?.Operations == null)
+                {
+                    continue;
+                }
+
+                foreach (OperationDescription operation in contract.Operations)
+                {
+                    // Presence of this behavior indicates the operation will use XmlSerializer at runtime.
+                    if (operation?.Behaviors?.Find<XmlSerializerOperationBehavior>() != null)
+                    {
+                        return true;
+                    }
+                }
+            }
+
+            return false;
+        }
+
+        private static void EmitInternalWithXmlSerializerWarningOnce()
+        {
+            if (Interlocked.Exchange(ref s_internalWithXmlSerializerWarningEmitted, 1) == 0)
+            {
+                ToolConsole.WriteWarning(SR.WrnInternalOptionPartiallyAppliedWithXmlSerializer);
+            }
+        }
+
         private static bool ContractsResolved(ServiceDescriptor serviceDescriptor, CodeCompileUnit codeCompileUnit)
         {
             if (serviceDescriptor != null && codeCompileUnit != null)
@@ -339,9 +387,9 @@ private static void AddStateForXmlSerializerImport(CommandProcessorOptions optio
                 if (options.EnableDataBinding == true)
                     importOptions.WebReferenceOptions.CodeGenerationOptions |= CodeGenerationOptions.EnableDataBinding;
 
-                // Right now System.Data API not available in DNX. If it comes available we could consider uncommenting these.
-                // importOptions.WebReferenceOptions.SchemaImporterExtensions.Add(typeof(TypedDataSetSchemaImporterExtensionFx35).AssemblyQualifiedName);
-                // importOptions.WebReferenceOptions.SchemaImporterExtensions.Add(typeof(DataSetSchemaImporterExtension).AssemblyQualifiedName);
+                // Enable a minimal schema importer extension for DataSet/DataTable.
+                // This avoids generating placeholder IXmlSerializable + ArrayOfXElement types for common DataSet wrapper patterns.
+                importOptions.WebReferenceOptions.SchemaImporterExtensions.Add(typeof(DataSetSchemaImporterExtension).AssemblyQualifiedName);
 
                 importOptions.CodeProvider = options.CodeProvider;
 
diff --git a/src/dotnet-svcutil/lib/src/SR.resx b/src/dotnet-svcutil/lib/src/SR.resx
index 39db9b0038e..4bb86359434 100644
--- a/src/dotnet-svcutil/lib/src/SR.resx
+++ b/src/dotnet-svcutil/lib/src/SR.resx
@@ -549,6 +549,9 @@ Your credentials will be sent to the server in clear text.</value>
   <data name="WrnCouldNotGenerateContractOperationsFormat" xml:space="preserve">
     <value>Could not generate contract operations using the '{0}' type, attempting with the '{1}' type.</value>
   </data>
+  <data name="WrnInternalOptionPartiallyAppliedWithXmlSerializer" xml:space="preserve">
+    <value>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</value>
+  </data>
   <data name="TelemetryEnabled" xml:space="preserve">
     <value>This tool collects information about how it is used in order to improve the tool. This functionality can be disabled by setting the environment variable "DOTNET_SVCUTIL_TELEMETRY_OPTOUT" to 1.
 </value>
diff --git a/src/dotnet-svcutil/lib/src/SchemaImporterExtensions/DataSetSchemaImporterExtension.cs b/src/dotnet-svcutil/lib/src/SchemaImporterExtensions/DataSetSchemaImporterExtension.cs
new file mode 100644
index 00000000000..f7bd0f154e0
--- /dev/null
+++ b/src/dotnet-svcutil/lib/src/SchemaImporterExtensions/DataSetSchemaImporterExtension.cs
@@ -0,0 +1,394 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Microsoft.CodeDom;
+using Microsoft.CodeDom.Compiler;
+using Microsoft.Xml;
+using Microsoft.Xml.Schema;
+using Microsoft.Xml.Serialization;
+using Microsoft.Xml.Serialization.Advanced;
+
+using System;
+
+namespace Microsoft.Tools.ServiceModel.Svcutil
+{
+    /// <summary>
+    /// Minimal schema importer extension that recognizes the common msdata annotations used to represent
+    /// ADO.NET DataSet/DataTable in WSDL/XSD and maps them to System.Data types.
+    ///
+    /// This intentionally avoids any dependency on System.Data internals and does not attempt to generate
+    /// typed datasets; it only returns the CLR type name to use.
+    /// </summary>
+    internal sealed class DataSetSchemaImporterExtension : SchemaImporterExtension
+    {
+        private const string MsDataNamespace = "urn:schemas-microsoft-com:xml-msdata";
+        private const string DiffgramNamespace = "urn:schemas-microsoft-com:xml-diffgram-v1";
+
+        // Common msdata attributes seen in DataSet/DataTable schema exports.
+        private const string AttrIsDataSet = "IsDataSet";
+        private const string AttrDataType = "DataType";
+        private static readonly string[] s_dataTableHints =
+        {
+            // Typed DataTable hints (a subset; we only need a signal, not full fidelity).
+            "GeneratorDataTableName",
+            "GeneratorUserTableName",
+            "GeneratorTableClassName",
+            "GeneratorTableVarName",
+        };
+
+        // Keep strings to avoid compile-time references to System.Data assemblies.
+        private const string DataSetClrTypeName = "System.Data.DataSet";
+        private const string DataTableClrTypeName = "System.Data.DataTable";
+
+        // Note: SchemaImporterExtensionCollection creates extensions via Activator.CreateInstance(type),
+        // so we keep a public parameterless constructor even though the type itself is internal.
+        public DataSetSchemaImporterExtension()
+        {
+        }
+
+        public override string ImportSchemaType(
+            string name,
+            string ns,
+            XmlSchemaObject context,
+            XmlSchemas schemas,
+            XmlSchemaImporter importer,
+            CodeCompileUnit compileUnit,
+            CodeNamespace mainNamespace,
+            CodeGenerationOptions options,
+            CodeDomProvider codeProvider)
+        {
+            // Some import paths call this overload. We can still decide based on the schema context annotations.
+            if (LooksLikeDataSetWrapperType(null, context))
+            {
+                return DataSetClrTypeName;
+            }
+
+            if (IsDataSetAnnotated(context))
+            {
+                return DataSetClrTypeName;
+            }
+
+            if (IsDataTableAnnotated(context))
+            {
+                return DataTableClrTypeName;
+            }
+
+            return null;
+        }
+
+        public override string ImportSchemaType(
+            XmlSchemaType type,
+            XmlSchemaObject context,
+            XmlSchemas schemas,
+            XmlSchemaImporter importer,
+            CodeCompileUnit compileUnit,
+            CodeNamespace mainNamespace,
+            CodeGenerationOptions options,
+            CodeDomProvider codeProvider)
+        {
+            // Heuristic fallback for schemas that don't include msdata annotations but use the classic
+            // "xsd:schema" + "xsd:any" wrapper pattern produced by DataSet exports.
+            // Example:
+            //   <xsd:sequence>
+            //     <xsd:element ref="xsd:schema" />
+            //     <xsd:any />
+            //   </xsd:sequence>
+            if (LooksLikeDataSetWrapperType(type, context))
+            {
+                return DataSetClrTypeName;
+            }
+
+            // Prefer context (often an element) and fall back to the type itself.
+            if (IsDataSetAnnotated(context) || IsDataSetAnnotated(type))
+            {
+                return DataSetClrTypeName;
+            }
+
+            if (IsDataTableAnnotated(context) || IsDataTableAnnotated(type))
+            {
+                return DataTableClrTypeName;
+            }
+
+            return null;
+        }
+
+        public override string ImportAnyElement(
+            XmlSchemaAny any,
+            bool mixed,
+            XmlSchemas schemas,
+            XmlSchemaImporter importer,
+            CodeCompileUnit compileUnit,
+            CodeNamespace mainNamespace,
+            CodeGenerationOptions options,
+            CodeDomProvider codeProvider)
+        {
+            // Some WSDLs carry msdata annotations directly on xs:any.
+            if (IsDataSetAnnotated(any))
+            {
+                return DataSetClrTypeName;
+            }
+
+            if (IsDataTableAnnotated(any))
+            {
+                return DataTableClrTypeName;
+            }
+
+            return null;
+        }
+
+        private static bool LooksLikeDataSetWrapperType(XmlSchemaType type, XmlSchemaObject context)
+        {
+            // First, try the provided type.
+            XmlSchemaComplexType complexType = type as XmlSchemaComplexType;
+
+            // If the type isn't directly provided (or isn't complex), try deriving it from the context.
+            if (complexType == null)
+            {
+                XmlSchemaElement element = context as XmlSchemaElement;
+                if (element != null)
+                {
+                    complexType = element.SchemaType as XmlSchemaComplexType;
+                }
+            }
+
+            if (complexType == null)
+            {
+                return false;
+            }
+
+            XmlSchemaSequence sequence = complexType.Particle as XmlSchemaSequence;
+            if (sequence == null || sequence.Items == null || sequence.Items.Count == 0)
+            {
+                return false;
+            }
+
+            bool hasSchemaRef = false;
+            bool hasSchemaAny = false;
+            bool hasAny = false;
+
+            // Ensure we only match the narrow "schema + any" wrapper pattern.
+            // If there are other particles, bail out.
+            for (int i = 0; i < sequence.Items.Count; i++)
+            {
+                XmlSchemaObject item = sequence.Items[i];
+
+                XmlSchemaElement itemElement = item as XmlSchemaElement;
+                if (itemElement != null)
+                {
+                    if (!itemElement.RefName.IsEmpty &&
+                        itemElement.RefName.Name == "schema" &&
+                        itemElement.RefName.Namespace == XmlSchema.Namespace)
+                    {
+                        hasSchemaRef = true;
+                        continue;
+                    }
+
+                    // Another common wrapper uses an explicit diffgram element reference instead of xs:any.
+                    //   <xs:element ref="diffgr:diffgram" />
+                    if (!itemElement.RefName.IsEmpty &&
+                        itemElement.RefName.Name == "diffgram" &&
+                        itemElement.RefName.Namespace == DiffgramNamespace)
+                    {
+                        hasAny = true;
+                        continue;
+                    }
+
+                    // Any other element means it's not the standard DataSet wrapper.
+                    return false;
+                }
+
+                XmlSchemaAny itemAny = item as XmlSchemaAny;
+                if (itemAny != null)
+                {
+                    // Another common DataSet wrapper is:
+                    //   <xs:any namespace="http://www.w3.org/2001/XMLSchema" />
+                    //   <xs:any namespace="urn:schemas-microsoft-com:xml-diffgram-v1" />
+                    // (or a second <xs:any/> without explicit namespace)
+                    if (itemAny.Namespace == XmlSchema.Namespace)
+                    {
+                        hasSchemaAny = true;
+                    }
+                    else
+                    {
+                        hasAny = true;
+                    }
+
+                    continue;
+                }
+
+                // Unknown particle.
+                return false;
+            }
+
+            return (hasSchemaRef || hasSchemaAny) && hasAny;
+        }
+
+        private static bool IsDataSetAnnotated(XmlSchemaObject schemaObject)
+        {
+            var value = GetMsDataValue(schemaObject, AttrIsDataSet);
+            if (value != null && value.Equals("true", StringComparison.OrdinalIgnoreCase))
+            {
+                return true;
+            }
+
+            // Some schemas use msdata:DataType="System.Data.DataSet" instead.
+            var dataType = GetMsDataValue(schemaObject, AttrDataType);
+            if (dataType != null &&
+                (dataType.Equals(DataSetClrTypeName, StringComparison.OrdinalIgnoreCase) ||
+                 dataType.EndsWith(".DataSet", StringComparison.OrdinalIgnoreCase)))
+            {
+                return true;
+            }
+
+            return false;
+        }
+
+        private static bool IsDataTableAnnotated(XmlSchemaObject schemaObject)
+        {
+            // DataTable does not have a single canonical marker, so we use a small set of common hints.
+            // We also explicitly avoid mapping to DataTable when IsDataSet==true.
+            if (IsDataSetAnnotated(schemaObject))
+            {
+                return false;
+            }
+
+            // Some schemas use msdata:DataType="System.Data.DataTable".
+            var dataType = GetMsDataValue(schemaObject, AttrDataType);
+            if (dataType != null &&
+                (dataType.Equals(DataTableClrTypeName, StringComparison.OrdinalIgnoreCase) ||
+                 dataType.EndsWith(".DataTable", StringComparison.OrdinalIgnoreCase)))
+            {
+                return true;
+            }
+
+            foreach (var hint in s_dataTableHints)
+            {
+                if (GetMsDataValue(schemaObject, hint) != null)
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        private static string GetMsDataValue(XmlSchemaObject schemaObject, string localName)
+        {
+            var fromAttributes = GetMsDataUnhandledAttributeValue(schemaObject, localName);
+            if (fromAttributes != null)
+            {
+                return fromAttributes;
+            }
+
+            return GetMsDataAppInfoValue(schemaObject, localName);
+        }
+
+        private static string GetMsDataUnhandledAttributeValue(XmlSchemaObject schemaObject, string localName)
+        {
+            XmlSchemaAnnotated annotated = schemaObject as XmlSchemaAnnotated;
+            if (annotated == null)
+                return null;
+
+            XmlAttribute[] attributes = annotated.UnhandledAttributes;
+            if (attributes == null || attributes.Length == 0)
+            {
+                return null;
+            }
+
+            for (int i = 0; i < attributes.Length; i++)
+            {
+                XmlAttribute attr = attributes[i];
+                if (attr == null)
+                {
+                    continue;
+                }
+
+                if (attr.NamespaceURI == MsDataNamespace && attr.LocalName == localName)
+                {
+                    return attr.Value;
+                }
+            }
+
+            return null;
+        }
+
+        private static string GetMsDataAppInfoValue(XmlSchemaObject schemaObject, string localName)
+        {
+            XmlSchemaAnnotated annotated = schemaObject as XmlSchemaAnnotated;
+            if (annotated == null)
+            {
+                return null;
+            }
+
+            XmlSchemaAnnotation annotation = annotated.Annotation;
+            if (annotation == null)
+            {
+                return null;
+            }
+
+            if (annotation.Items == null)
+            {
+                return null;
+            }
+
+            for (int i = 0; i < annotation.Items.Count; i++)
+            {
+                XmlSchemaAppInfo appInfo = annotation.Items[i] as XmlSchemaAppInfo;
+                if (appInfo == null || appInfo.Markup == null)
+                {
+                    continue;
+                }
+
+                for (int j = 0; j < appInfo.Markup.Length; j++)
+                {
+                    XmlNode node = appInfo.Markup[j];
+                    if (node == null)
+                    {
+                        continue;
+                    }
+
+                    // Match element form: <msdata:IsDataSet>true</msdata:IsDataSet>
+                    XmlElement element = node as XmlElement;
+                    if (element != null)
+                    {
+                        if (element.NamespaceURI == MsDataNamespace && element.LocalName == localName)
+                        {
+                            return element.InnerText;
+                        }
+
+                        // Some appinfo blocks put msdata annotations as attributes on arbitrary elements.
+                        if (element.Attributes != null)
+                        {
+                            for (int k = 0; k < element.Attributes.Count; k++)
+                            {
+                                XmlAttribute attr = element.Attributes[k];
+                                if (attr != null && attr.NamespaceURI == MsDataNamespace && attr.LocalName == localName)
+                                {
+                                    return attr.Value;
+                                }
+                            }
+                        }
+                    }
+                    else
+                    {
+                        // Generic fallback: scan attributes, if any.
+                        if (node.Attributes != null)
+                        {
+                            for (int k = 0; k < node.Attributes.Count; k++)
+                            {
+                                XmlAttribute attr = node.Attributes[k];
+                                if (attr != null && attr.NamespaceURI == MsDataNamespace && attr.LocalName == localName)
+                                {
+                                    return attr.Value;
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
+            return null;
+        }
+    }
+}
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.cs.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.cs.xlf
index 53fd7857951..2d0e81a727f 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.cs.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.cs.xlf
@@ -827,6 +827,11 @@ Pokud jste se pokoušeli vygenerovat klienta, může k tomuto dojít v případ
         <target state="translated">Koncový bod {0} na adrese {1} obsahuje nejméně jednu vazbu, která není kompatibilní s aplikacemi .NET Core. Přeskakování...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">Cílová architektura {0} se nepodporuje a v budoucnu už nebude dostávat aktualizace zabezpečení.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.de.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.de.xlf
index 31775ab3fe7..c050f793868 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.de.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.de.xlf
@@ -827,6 +827,11 @@ Wenn Sie versucht haben, einen Client zu generieren, könnte die Ursache hierfü
         <target state="translated">Der Endpunkt "{0}" an der Adresse "{1}" enthält mindestens eine Bindung, die nicht mit .NET Core-Apps kompatibel ist. Wird übersprungen...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">Das Zielframework "{0}" wird nicht mehr unterstützt und erhält in Zukunft keine Sicherheitsupdates mehr.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.es.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.es.xlf
index 10d1a0dd041..b4bbc991109 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.es.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.es.xlf
@@ -827,6 +827,11 @@ Si intentaba generar un cliente, es posible que se deba a que los documentos de
         <target state="translated">El punto de conexión "{0}" en la dirección "{1}" contiene uno o varios enlaces no compatibles con las aplicaciones de .Net Core, omitiendo...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">La plataforma de destino "{0}" no es compatible y no recibirá actualizaciones de seguridad en el futuro.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.fr.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.fr.xlf
index 66db4c81738..c6217db1f8a 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.fr.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.fr.xlf
@@ -827,6 +827,11 @@ Si vous avez tenté de générer un client, cela peut être dû au fait que les
         <target state="translated">Le point de terminaison '{0}' à l'adresse '{1}' contient une ou plusieurs liaisons non compatibles avec les applications .Net Core. Il va être ignoré...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">Le framework cible «{0}» n’est pas pris en charge et ne recevra pas de mises à jour de sécurité à l’avenir.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.it.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.it.xlf
index 16d90b20e4c..8c039dfba9a 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.it.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.it.xlf
@@ -827,6 +827,11 @@ Se si stava provando a creare un client, il problema può dipendere dal fatto ch
         <target state="translated">L'endpoint '{0}' all'indirizzo '{1}' contiene uno o più binding non compatibili con le app .NET Core. Verrà ignorato...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">Il supporto per il framework di destinazione '{0}' non è più disponibile e non riceverà gli aggiornamenti della sicurezza in futuro.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.ja.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.ja.xlf
index c9233a0e974..0e83c3b8ca5 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.ja.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.ja.xlf
@@ -827,6 +827,11 @@ If you were trying to generate a client, this could be because the metadata docu
         <target state="translated">アドレス '{1}' のエンドポイント '{0}' に、.Net Core アプリと互換性のないバインドが 1 つ以上含まれています。スキップしています...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">ターゲット フレームワーク '{0}' はサポート対象外で、今後、セキュリティ更新プログラムは受け取ることはありません。</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.ko.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.ko.xlf
index 485c6dc756e..df79c3b67ce 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.ko.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.ko.xlf
@@ -827,6 +827,11 @@ If you were trying to generate a client, this could be because the metadata docu
         <target state="translated">주소 '{1}'의 엔드포인트 '{0}'에 .NET Core 앱과 호환되지 않는 바인딩이 하나 이상 있습니다. 건너뜁니다.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">대상 프레임워크 '{0}'은(는) 지원되지 않으며 향후 보안 업데이트를 받지 않습니다.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.pl.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.pl.xlf
index 840f98a138f..f761c161994 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.pl.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.pl.xlf
@@ -827,6 +827,11 @@ Jeśli próbowano wygenerować klienta, może być to spowodowane przez dokument
         <target state="translated">Punkt końcowy „{0}” pod adresem „{1}” zawiera co najmniej jedno powiązanie, które nie jest zgodne z aplikacjami .Net Core. Są one pomijane...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">Platforma docelowa „{0}” nie jest obsługiwana i w przyszłości nie będzie otrzymywać aktualizacji zabezpieczeń.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.pt-BR.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.pt-BR.xlf
index 343a85ffdc5..01a14cfc559 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.pt-BR.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.pt-BR.xlf
@@ -827,6 +827,11 @@ Se você estava tentando gerar um cliente, isso pode ter acontecido porque os do
         <target state="translated">O ponto de extremidade '{0}' no endereço '{1}' contém uma ou mais associações não compatíveis com os aplicativos .Net Core. Ignorando...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">A estrutura de destino '{0}' está sem suporte e não receberá atualizações de segurança no futuro.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.ru.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.ru.xlf
index 02186b1bccc..8b35a8f61d5 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.ru.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.ru.xlf
@@ -827,6 +827,11 @@ If you were trying to generate a client, this could be because the metadata docu
         <target state="translated">Конечная точка "{0}" по адресу "{1}" содержит одну или несколько привязок, несовместимых с приложениями .Net Core. Пропуск...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">Требуемая версия .NET Framework "{0}" больше не поддерживается и не будет получать обновления для системы безопасности.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.tr.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.tr.xlf
index e5baaaa661c..4e7fff2fd33 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.tr.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.tr.xlf
@@ -827,6 +827,11 @@ If you were trying to generate a client, this could be because the metadata docu
         <target state="translated">'{1}' adresindeki '{0}' uç noktası, .Net Core uygulamalarıyla uyumsuz bir veya daha fazla bağlama içerdiğinden atlanıyor...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">'{0}' hedef çerçevesi destek kapsamı dışında olduğu için gelecekte güvenlik güncelleştirmeleri almayacak.</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.zh-Hans.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.zh-Hans.xlf
index ae4d13d4f51..1cdfb2d92f4 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.zh-Hans.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.zh-Hans.xlf
@@ -827,6 +827,11 @@ If you were trying to generate a client, this could be because the metadata docu
         <target state="translated">地址“{1}”处的终结点“{0}”包含一个或多个与 .Net Core 应用不兼容的绑定，正在跳过...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">目标框架“{0}”已失去支持，并且将来不会收到安全更新。</target>
diff --git a/src/dotnet-svcutil/lib/src/xlf/SR.zh-Hant.xlf b/src/dotnet-svcutil/lib/src/xlf/SR.zh-Hant.xlf
index 0f3492fbcf7..5603b618e15 100644
--- a/src/dotnet-svcutil/lib/src/xlf/SR.zh-Hant.xlf
+++ b/src/dotnet-svcutil/lib/src/xlf/SR.zh-Hant.xlf
@@ -827,6 +827,11 @@ If you were trying to generate a client, this could be because the metadata docu
         <target state="translated">位於位址 '{1}' 的端點 '{0}' 包含一或多個與 .Net Core 應用程式不相容的繫結，將會跳過...</target>
         <note />
       </trans-unit>
+      <trans-unit id="WrnInternalOptionPartiallyAppliedWithXmlSerializer">
+        <source>--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</source>
+        <target state="new">--internal may be only partially applied when using XmlSerializer; some schema wrapper types are generated as public for runtime compatibility.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WrnOutOfSupportTargetFrameworkFormat">
         <source>The target framework '{0}' is out of support and will not receive security updates in the future.</source>
         <target state="translated">已不支援目標 Framework '{0}'，未來將不會收到安全性更新。</target>
diff --git a/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper.csproj b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper.csproj
new file mode 100644
index 00000000000..c2d91e178fd
--- /dev/null
+++ b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper.csproj
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>N.N</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="System.ServiceModel.*", Version="N.N.N">
+    <PackageReference Include="System.ServiceModel.*", Version="N.N.N">
+    <PackageReference Include="System.ServiceModel.*", Version="N.N.N">
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/Reference.cs b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/Reference.cs
new file mode 100644
index 00000000000..85520ebabe1
--- /dev/null
+++ b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/Reference.cs
@@ -0,0 +1,189 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by a tool.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+namespace InternalTypes_DataSetWrapper_NS
+{
+    
+    
+    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "99.99.99")]
+    [System.ServiceModel.ServiceContractAttribute(Namespace="http://tempuri.org", ConfigurationName="InternalTypes_DataSetWrapper_NS.MyServiceSoap")]
+    internal interface MyServiceSoap
+    {
+        
+        [System.ServiceModel.OperationContractAttribute(Action="http://tempuri.org/GetData", ReplyAction="*")]
+        [System.ServiceModel.XmlSerializerFormatAttribute(SupportFaults=true)]
+        System.Threading.Tasks.Task<InternalTypes_DataSetWrapper_NS.Data> GetDataAsync();
+    }
+    
+    /// <remarks/>
+    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "99.99.99")]
+    [System.Diagnostics.DebuggerStepThroughAttribute()]
+    [System.Xml.Serialization.XmlTypeAttribute(Namespace="http://tempuri.org")]
+    [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverageAttribute()]
+    public partial class Data
+    {
+        
+        private int dataIdField;
+        
+        private System.Data.DataSet dataRecordsField;
+        
+        private string noteField;
+        
+        /// <remarks/>
+        [System.Xml.Serialization.XmlElementAttribute(Order=0)]
+        public int DataId
+        {
+            get
+            {
+                return this.dataIdField;
+            }
+            set
+            {
+                this.dataIdField = value;
+            }
+        }
+        
+        /// <remarks/>
+        [System.Xml.Serialization.XmlElementAttribute(Order=1)]
+        public System.Data.DataSet DataRecords
+        {
+            get
+            {
+                return this.dataRecordsField;
+            }
+            set
+            {
+                this.dataRecordsField = value;
+            }
+        }
+        
+        /// <remarks/>
+        [System.Xml.Serialization.XmlElementAttribute(Order=2)]
+        public string Note
+        {
+            get
+            {
+                return this.noteField;
+            }
+            set
+            {
+                this.noteField = value;
+            }
+        }
+    }
+    
+    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "99.99.99")]
+    internal interface MyServiceSoapChannel : InternalTypes_DataSetWrapper_NS.MyServiceSoap, System.ServiceModel.IClientChannel
+    {
+    }
+    
+    [System.Diagnostics.DebuggerStepThroughAttribute()]
+    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "99.99.99")]
+    [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverageAttribute()]
+    internal partial class MyServiceSoapClient : System.ServiceModel.ClientBase<InternalTypes_DataSetWrapper_NS.MyServiceSoap>, InternalTypes_DataSetWrapper_NS.MyServiceSoap
+    {
+        
+        /// <summary>
+        /// Implement this partial method to configure the service endpoint.
+        /// </summary>
+        /// <param name="serviceEndpoint">The endpoint to configure</param>
+        /// <param name="clientCredentials">The client credentials</param>
+        static partial void ConfigureEndpoint(System.ServiceModel.Description.ServiceEndpoint serviceEndpoint, System.ServiceModel.Description.ClientCredentials clientCredentials);
+        
+        public MyServiceSoapClient() : 
+                base(MyServiceSoapClient.GetDefaultBinding(), MyServiceSoapClient.GetDefaultEndpointAddress())
+        {
+            this.Endpoint.Name = EndpointConfiguration.MyServiceSoap.ToString();
+            ConfigureEndpoint(this.Endpoint, this.ClientCredentials);
+        }
+        
+        public MyServiceSoapClient(EndpointConfiguration endpointConfiguration) : 
+                base(MyServiceSoapClient.GetBindingForEndpoint(endpointConfiguration), MyServiceSoapClient.GetEndpointAddress(endpointConfiguration))
+        {
+            this.Endpoint.Name = endpointConfiguration.ToString();
+            ConfigureEndpoint(this.Endpoint, this.ClientCredentials);
+        }
+        
+        public MyServiceSoapClient(EndpointConfiguration endpointConfiguration, string remoteAddress) : 
+                base(MyServiceSoapClient.GetBindingForEndpoint(endpointConfiguration), new System.ServiceModel.EndpointAddress(remoteAddress))
+        {
+            this.Endpoint.Name = endpointConfiguration.ToString();
+            ConfigureEndpoint(this.Endpoint, this.ClientCredentials);
+        }
+        
+        public MyServiceSoapClient(EndpointConfiguration endpointConfiguration, System.ServiceModel.EndpointAddress remoteAddress) : 
+                base(MyServiceSoapClient.GetBindingForEndpoint(endpointConfiguration), remoteAddress)
+        {
+            this.Endpoint.Name = endpointConfiguration.ToString();
+            ConfigureEndpoint(this.Endpoint, this.ClientCredentials);
+        }
+        
+        public MyServiceSoapClient(System.ServiceModel.Channels.Binding binding, System.ServiceModel.EndpointAddress remoteAddress) : 
+                base(binding, remoteAddress)
+        {
+        }
+        
+        public System.Threading.Tasks.Task<InternalTypes_DataSetWrapper_NS.Data> GetDataAsync()
+        {
+            return base.Channel.GetDataAsync();
+        }
+        
+        public virtual System.Threading.Tasks.Task OpenAsync()
+        {
+            return System.Threading.Tasks.Task.Factory.FromAsync(((System.ServiceModel.ICommunicationObject)(this)).BeginOpen(null, null), new System.Action<System.IAsyncResult>(((System.ServiceModel.ICommunicationObject)(this)).EndOpen));
+        }
+        
+        #if !NET6_0_OR_GREATER
+        public virtual System.Threading.Tasks.Task CloseAsync()
+        {
+            return System.Threading.Tasks.Task.Factory.FromAsync(((System.ServiceModel.ICommunicationObject)(this)).BeginClose(null, null), new System.Action<System.IAsyncResult>(((System.ServiceModel.ICommunicationObject)(this)).EndClose));
+        }
+        #endif
+        
+        private static System.ServiceModel.Channels.Binding GetBindingForEndpoint(EndpointConfiguration endpointConfiguration)
+        {
+            if ((endpointConfiguration == EndpointConfiguration.MyServiceSoap))
+            {
+                System.ServiceModel.BasicHttpBinding result = new System.ServiceModel.BasicHttpBinding();
+                result.MaxBufferSize = int.MaxValue;
+                result.ReaderQuotas = System.Xml.XmlDictionaryReaderQuotas.Max;
+                result.MaxReceivedMessageSize = int.MaxValue;
+                result.AllowCookies = true;
+                result.Security.Mode = System.ServiceModel.BasicHttpSecurityMode.Transport;
+                return result;
+            }
+            throw new System.InvalidOperationException(string.Format("Could not find endpoint with name \'{0}\'.", endpointConfiguration));
+        }
+        
+        private static System.ServiceModel.EndpointAddress GetEndpointAddress(EndpointConfiguration endpointConfiguration)
+        {
+            if ((endpointConfiguration == EndpointConfiguration.MyServiceSoap))
+            {
+                return new System.ServiceModel.EndpointAddress("https://contoso.com/MyService.svc");
+            }
+            throw new System.InvalidOperationException(string.Format("Could not find endpoint with name \'{0}\'.", endpointConfiguration));
+        }
+        
+        private static System.ServiceModel.Channels.Binding GetDefaultBinding()
+        {
+            return MyServiceSoapClient.GetBindingForEndpoint(EndpointConfiguration.MyServiceSoap);
+        }
+        
+        private static System.ServiceModel.EndpointAddress GetDefaultEndpointAddress()
+        {
+            return MyServiceSoapClient.GetEndpointAddress(EndpointConfiguration.MyServiceSoap);
+        }
+        
+        public enum EndpointConfiguration
+        {
+            
+            MyServiceSoap,
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/dotnet-svcutil.params.json b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/dotnet-svcutil.params.json
new file mode 100644
index 00000000000..e95476218a9
--- /dev/null
+++ b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper/dotnet-svcutil.params.json
@@ -0,0 +1,16 @@
+{
+  "providerId": "Microsoft.Tools.ServiceModel.Svcutil",
+  "version": "99.99.99",
+  "options": {
+    "inputs": [
+      "../../../../../src/dotnet-svcutil/lib/tests/TestCases/wsdl/InternalTypes_DataSetWrapper.wsdl"
+    ],
+    "internalTypeAccess": true,
+    "namespaceMappings": [
+      "*, InternalTypes_DataSetWrapper_NS"
+    ],
+    "outputFile": "Reference.cs",
+    "targetFramework": "N.N",
+    "typeReuseMode": "None"
+  }
+}
\ No newline at end of file
diff --git a/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/InternalTypes_DataSetWrapper_NoInternal.csproj b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/InternalTypes_DataSetWrapper_NoInternal.csproj
new file mode 100644
index 00000000000..c2d91e178fd
--- /dev/null
+++ b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/InternalTypes_DataSetWrapper_NoInternal.csproj
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>N.N</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+  <ItemGroup>
+    <PackageReference Include="System.ServiceModel.*", Version="N.N.N">
+    <PackageReference Include="System.ServiceModel.*", Version="N.N.N">
+    <PackageReference Include="System.ServiceModel.*", Version="N.N.N">
+  </ItemGroup>
+</Project>
\ No newline at end of file
diff --git a/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/Reference.cs b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/Reference.cs
new file mode 100644
index 00000000000..3c202141076
--- /dev/null
+++ b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/Reference.cs
@@ -0,0 +1,189 @@
+//------------------------------------------------------------------------------
+// <auto-generated>
+//     This code was generated by a tool.
+//
+//     Changes to this file may cause incorrect behavior and will be lost if
+//     the code is regenerated.
+// </auto-generated>
+//------------------------------------------------------------------------------
+
+namespace InternalTypes_DataSetWrapper_NoInternal_NS
+{
+    
+    
+    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "99.99.99")]
+    [System.ServiceModel.ServiceContractAttribute(Namespace="http://tempuri.org", ConfigurationName="InternalTypes_DataSetWrapper_NoInternal_NS.MyServiceSoap")]
+    public interface MyServiceSoap
+    {
+        
+        [System.ServiceModel.OperationContractAttribute(Action="http://tempuri.org/GetData", ReplyAction="*")]
+        [System.ServiceModel.XmlSerializerFormatAttribute(SupportFaults=true)]
+        System.Threading.Tasks.Task<InternalTypes_DataSetWrapper_NoInternal_NS.Data> GetDataAsync();
+    }
+    
+    /// <remarks/>
+    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "99.99.99")]
+    [System.Diagnostics.DebuggerStepThroughAttribute()]
+    [System.Xml.Serialization.XmlTypeAttribute(Namespace="http://tempuri.org")]
+    [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverageAttribute()]
+    public partial class Data
+    {
+        
+        private int dataIdField;
+        
+        private System.Data.DataSet dataRecordsField;
+        
+        private string noteField;
+        
+        /// <remarks/>
+        [System.Xml.Serialization.XmlElementAttribute(Order=0)]
+        public int DataId
+        {
+            get
+            {
+                return this.dataIdField;
+            }
+            set
+            {
+                this.dataIdField = value;
+            }
+        }
+        
+        /// <remarks/>
+        [System.Xml.Serialization.XmlElementAttribute(Order=1)]
+        public System.Data.DataSet DataRecords
+        {
+            get
+            {
+                return this.dataRecordsField;
+            }
+            set
+            {
+                this.dataRecordsField = value;
+            }
+        }
+        
+        /// <remarks/>
+        [System.Xml.Serialization.XmlElementAttribute(Order=2)]
+        public string Note
+        {
+            get
+            {
+                return this.noteField;
+            }
+            set
+            {
+                this.noteField = value;
+            }
+        }
+    }
+    
+    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "99.99.99")]
+    public interface MyServiceSoapChannel : InternalTypes_DataSetWrapper_NoInternal_NS.MyServiceSoap, System.ServiceModel.IClientChannel
+    {
+    }
+    
+    [System.Diagnostics.DebuggerStepThroughAttribute()]
+    [System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Tools.ServiceModel.Svcutil", "99.99.99")]
+    [System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverageAttribute()]
+    public partial class MyServiceSoapClient : System.ServiceModel.ClientBase<InternalTypes_DataSetWrapper_NoInternal_NS.MyServiceSoap>, InternalTypes_DataSetWrapper_NoInternal_NS.MyServiceSoap
+    {
+        
+        /// <summary>
+        /// Implement this partial method to configure the service endpoint.
+        /// </summary>
+        /// <param name="serviceEndpoint">The endpoint to configure</param>
+        /// <param name="clientCredentials">The client credentials</param>
+        static partial void ConfigureEndpoint(System.ServiceModel.Description.ServiceEndpoint serviceEndpoint, System.ServiceModel.Description.ClientCredentials clientCredentials);
+        
+        public MyServiceSoapClient() : 
+                base(MyServiceSoapClient.GetDefaultBinding(), MyServiceSoapClient.GetDefaultEndpointAddress())
+        {
+            this.Endpoint.Name = EndpointConfiguration.MyServiceSoap.ToString();
+            ConfigureEndpoint(this.Endpoint, this.ClientCredentials);
+        }
+        
+        public MyServiceSoapClient(EndpointConfiguration endpointConfiguration) : 
+                base(MyServiceSoapClient.GetBindingForEndpoint(endpointConfiguration), MyServiceSoapClient.GetEndpointAddress(endpointConfiguration))
+        {
+            this.Endpoint.Name = endpointConfiguration.ToString();
+            ConfigureEndpoint(this.Endpoint, this.ClientCredentials);
+        }
+        
+        public MyServiceSoapClient(EndpointConfiguration endpointConfiguration, string remoteAddress) : 
+                base(MyServiceSoapClient.GetBindingForEndpoint(endpointConfiguration), new System.ServiceModel.EndpointAddress(remoteAddress))
+        {
+            this.Endpoint.Name = endpointConfiguration.ToString();
+            ConfigureEndpoint(this.Endpoint, this.ClientCredentials);
+        }
+        
+        public MyServiceSoapClient(EndpointConfiguration endpointConfiguration, System.ServiceModel.EndpointAddress remoteAddress) : 
+                base(MyServiceSoapClient.GetBindingForEndpoint(endpointConfiguration), remoteAddress)
+        {
+            this.Endpoint.Name = endpointConfiguration.ToString();
+            ConfigureEndpoint(this.Endpoint, this.ClientCredentials);
+        }
+        
+        public MyServiceSoapClient(System.ServiceModel.Channels.Binding binding, System.ServiceModel.EndpointAddress remoteAddress) : 
+                base(binding, remoteAddress)
+        {
+        }
+        
+        public System.Threading.Tasks.Task<InternalTypes_DataSetWrapper_NoInternal_NS.Data> GetDataAsync()
+        {
+            return base.Channel.GetDataAsync();
+        }
+        
+        public virtual System.Threading.Tasks.Task OpenAsync()
+        {
+            return System.Threading.Tasks.Task.Factory.FromAsync(((System.ServiceModel.ICommunicationObject)(this)).BeginOpen(null, null), new System.Action<System.IAsyncResult>(((System.ServiceModel.ICommunicationObject)(this)).EndOpen));
+        }
+        
+        #if !NET6_0_OR_GREATER
+        public virtual System.Threading.Tasks.Task CloseAsync()
+        {
+            return System.Threading.Tasks.Task.Factory.FromAsync(((System.ServiceModel.ICommunicationObject)(this)).BeginClose(null, null), new System.Action<System.IAsyncResult>(((System.ServiceModel.ICommunicationObject)(this)).EndClose));
+        }
+        #endif
+        
+        private static System.ServiceModel.Channels.Binding GetBindingForEndpoint(EndpointConfiguration endpointConfiguration)
+        {
+            if ((endpointConfiguration == EndpointConfiguration.MyServiceSoap))
+            {
+                System.ServiceModel.BasicHttpBinding result = new System.ServiceModel.BasicHttpBinding();
+                result.MaxBufferSize = int.MaxValue;
+                result.ReaderQuotas = System.Xml.XmlDictionaryReaderQuotas.Max;
+                result.MaxReceivedMessageSize = int.MaxValue;
+                result.AllowCookies = true;
+                result.Security.Mode = System.ServiceModel.BasicHttpSecurityMode.Transport;
+                return result;
+            }
+            throw new System.InvalidOperationException(string.Format("Could not find endpoint with name \'{0}\'.", endpointConfiguration));
+        }
+        
+        private static System.ServiceModel.EndpointAddress GetEndpointAddress(EndpointConfiguration endpointConfiguration)
+        {
+            if ((endpointConfiguration == EndpointConfiguration.MyServiceSoap))
+            {
+                return new System.ServiceModel.EndpointAddress("https://contoso.com/MyService.svc");
+            }
+            throw new System.InvalidOperationException(string.Format("Could not find endpoint with name \'{0}\'.", endpointConfiguration));
+        }
+        
+        private static System.ServiceModel.Channels.Binding GetDefaultBinding()
+        {
+            return MyServiceSoapClient.GetBindingForEndpoint(EndpointConfiguration.MyServiceSoap);
+        }
+        
+        private static System.ServiceModel.EndpointAddress GetDefaultEndpointAddress()
+        {
+            return MyServiceSoapClient.GetEndpointAddress(EndpointConfiguration.MyServiceSoap);
+        }
+        
+        public enum EndpointConfiguration
+        {
+            
+            MyServiceSoap,
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/dotnet-svcutil.params.json b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/dotnet-svcutil.params.json
new file mode 100644
index 00000000000..229a16d2d76
--- /dev/null
+++ b/src/dotnet-svcutil/lib/tests/Baselines/InternalTypes_DataSetWrapper/InternalTypes_DataSetWrapper_NoInternal/dotnet-svcutil.params.json
@@ -0,0 +1,15 @@
+{
+  "providerId": "Microsoft.Tools.ServiceModel.Svcutil",
+  "version": "99.99.99",
+  "options": {
+    "inputs": [
+      "../../../../../src/dotnet-svcutil/lib/tests/TestCases/wsdl/InternalTypes_DataSetWrapper.wsdl"
+    ],
+    "namespaceMappings": [
+      "*, InternalTypes_DataSetWrapper_NoInternal_NS"
+    ],
+    "outputFile": "Reference.cs",
+    "targetFramework": "N.N",
+    "typeReuseMode": "None"
+  }
+}
\ No newline at end of file
diff --git a/src/dotnet-svcutil/lib/tests/TestCases/wsdl/InternalTypes_DataSetWrapper.wsdl b/src/dotnet-svcutil/lib/tests/TestCases/wsdl/InternalTypes_DataSetWrapper.wsdl
new file mode 100644
index 00000000000..23933f63f57
--- /dev/null
+++ b/src/dotnet-svcutil/lib/tests/TestCases/wsdl/InternalTypes_DataSetWrapper.wsdl
@@ -0,0 +1,60 @@
+<?xml version="1.0" encoding="utf-8"?>
+<wsdl:definitions xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:mime="http://schemas.xmlsoap.org/wsdl/mime/" xmlns:tns="http://tempuri.org" xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/" xmlns:s="http://www.w3.org/2001/XMLSchema" targetNamespace="http://tempuri.org" xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">
+  <wsdl:types>
+    <s:schema elementFormDefault="qualified" targetNamespace="http://tempuri.org">
+      <s:complexType name="Data">
+        <s:sequence>
+          <s:element minOccurs="1" maxOccurs="1" name="DataId" type="s:int" />
+          <s:element minOccurs="0" maxOccurs="1" name="DataRecords">
+            <s:complexType>
+              <s:sequence>
+                <s:element ref="s:schema" />
+                <s:any />
+              </s:sequence>
+            </s:complexType>
+          </s:element>
+          <s:element minOccurs="0" maxOccurs="1" name="Note" type="s:string" />
+        </s:sequence>
+      </s:complexType>
+      <s:element name="GetData">
+        <s:complexType />
+      </s:element>
+      <s:element name="GetDataResponse">
+        <s:complexType>
+          <s:sequence>
+            <s:element minOccurs="0" maxOccurs="1" name="GetDataResult" type="tns:Data" />
+          </s:sequence>
+        </s:complexType>
+      </s:element>
+    </s:schema>
+  </wsdl:types>
+  <wsdl:message name="GetDataSoapIn">
+    <wsdl:part name="parameters" element="tns:GetData" />
+  </wsdl:message>
+  <wsdl:message name="GetDataSoapOut">
+    <wsdl:part name="parameters" element="tns:GetDataResponse" />
+  </wsdl:message>
+  <wsdl:portType name="MyServiceSoap">
+    <wsdl:operation name="GetData">
+      <wsdl:input message="tns:GetDataSoapIn" />
+      <wsdl:output message="tns:GetDataSoapOut" />
+    </wsdl:operation>
+  </wsdl:portType>
+  <wsdl:binding name="MyServiceSoap" type="tns:MyServiceSoap">
+    <soap:binding transport="http://schemas.xmlsoap.org/soap/http" />
+    <wsdl:operation name="GetData">
+      <soap:operation soapAction="http://tempuri.org/GetData" style="document" />
+      <wsdl:input>
+        <soap:body use="literal" />
+      </wsdl:input>
+      <wsdl:output>
+        <soap:body use="literal" />
+      </wsdl:output>
+    </wsdl:operation>
+  </wsdl:binding>
+  <wsdl:service name="MyService">
+    <wsdl:port name="MyServiceSoap" binding="tns:MyServiceSoap">
+      <soap:address location="https://contoso.com/MyService.svc" />
+    </wsdl:port>
+  </wsdl:service>
+</wsdl:definitions>
diff --git a/src/dotnet-svcutil/lib/tests/src/GlobalToolTests.cs b/src/dotnet-svcutil/lib/tests/src/GlobalToolTests.cs
index 6485d77a416..14cfa85e46f 100644
--- a/src/dotnet-svcutil/lib/tests/src/GlobalToolTests.cs
+++ b/src/dotnet-svcutil/lib/tests/src/GlobalToolTests.cs
@@ -4,6 +4,7 @@
 
 using System;
 using System.IO;
+using System.Linq;
 using Microsoft.Tools.ServiceModel.Svcutil;
 using System.Threading;
 using Xunit;
@@ -13,6 +14,14 @@ namespace SvcutilTest
 {
     public partial class E2ETest
     {
+        private static int CountInternalXmlSerializerWarningLines(string outputText)
+        {
+            return outputText
+                .Split(new[] { "\r\n", "\n" }, StringSplitOptions.None)
+                .Count(l => l.IndexOf("--internal", StringComparison.OrdinalIgnoreCase) >= 0 &&
+                            l.IndexOf("XmlSerializer", StringComparison.OrdinalIgnoreCase) >= 0);
+        }
+
         private void TestGlobalSvcutil(string options, bool expectSuccess = true)
         {
             Assert.False(string.IsNullOrWhiteSpace(this_TestCaseName), $"{nameof(this_TestCaseName)} not initialized!");
@@ -57,6 +66,42 @@ public void LanguageOption(string lang)
             TestGlobalSvcutil(options);
         }
 
+        [Trait("Category", "Test")]
+        [Theory]
+        [InlineData("InternalTypes_DataSetWrapper_NoInternal", false, 0)]
+        [InlineData("InternalTypes_DataSetWrapper", true, 1)]
+        public void InternalTypes_DataSetWrapper_Variations(string testCaseName, bool useInternal, int expectedWarningCount)
+        {
+            // Validate both default (public) and --internal flows for the same WSDL.
+            // Note: this test will require baselines for both variations.
+            const string groupName = "InternalTypes_DataSetWrapper";
+            this_TestCaseName = groupName;
+            TestFixture();
+
+            this_TestCaseName = testCaseName;
+            InitializeGlobal(testCaseName);
+
+            var wsdlFile = Path.Combine(g_TestCasesDir, "wsdl", "InternalTypes_DataSetWrapper.wsdl");
+
+            // Do not force a serializer. This matches real user behavior and validates the default code path.
+            var options = useInternal
+                ? $"\"{wsdlFile}\" -i -nl"
+                : $"\"{wsdlFile}\" -nl";
+
+            options = AppendCommonOptions(options);
+            var processResult = this_TestCaseProject.RunSvcutil(options, expectSuccess: true, this_TestCaseLogger, globalTool: true);
+
+            Assert.True(processResult.ExitCode == 0 || processResult.ExitCode == 6, processResult.OutputText);
+
+            // Assert on invariant tokens so the test is resilient to localization.
+            var warningCount = CountInternalXmlSerializerWarningLines(processResult.OutputText);
+            Assert.True(
+                warningCount == expectedWarningCount,
+                $"Expected {expectedWarningCount} warning(s) mentioning both '--internal' and 'XmlSerializer', found {warningCount}. Output was:{Environment.NewLine}{processResult.OutputText}");
+
+            ValidateTest(options, this_TestCaseProject.DirectoryPath, processResult.ExitCode, processResult.OutputText, expectSuccess: true);
+        }
+
         [Theory]
         [Trait("Category", "BVT")]
         [InlineData("Project", "--toolContext Project -ntr -tf netcoreapp2.0 -nb")]