diff --git a/milter/entrypoint.sh b/milter/entrypoint.sh
index 3bf9c43..8fed8f3 100644
--- a/milter/entrypoint.sh
+++ b/milter/entrypoint.sh
@@ -149,11 +149,19 @@ fi
 if [ "${OTEL_TRACING_ENABLED:-false}" = "true" ]; then
     export OTEL_SERVICE_NAME="${OTEL_SERVICE_NAME:-milter}"
     export OTEL_EXPORTER_OTLP_ENDPOINT="${OTEL_EXPORTER_OTLP_ENDPOINT:-http://localhost:4318}"
+    # The Dockerfile installs only the HTTP variant of the OTLP exporter
+    # (opentelemetry-exporter-otlp-proto-http). The OTel spec defaults
+    # the protocol to grpc, which makes opentelemetry-instrument try
+    # to load a gRPC exporter that isn't installed and raise:
+    #   "Requested component 'otlp_proto_grpc' not found in entry
+    #    point 'opentelemetry_traces_exporter'"
+    # Pin the protocol so the right exporter is selected.
+    export OTEL_EXPORTER_OTLP_PROTOCOL="${OTEL_EXPORTER_OTLP_PROTOCOL:-http/protobuf}"
     # tracecontext + baggage are the W3C-standard propagators; matches what
     # ddtrace emits when DD_TRACE_PROPAGATION_STYLE includes tracecontext, so
     # cross-service trace continuity holds regardless of which SDK is active.
     export OTEL_PROPAGATORS="${OTEL_PROPAGATORS:-tracecontext,baggage}"
-    echo "OpenTelemetry tracing enabled (service=${OTEL_SERVICE_NAME}, endpoint=${OTEL_EXPORTER_OTLP_ENDPOINT})"
+    echo "OpenTelemetry tracing enabled (service=${OTEL_SERVICE_NAME}, endpoint=${OTEL_EXPORTER_OTLP_ENDPOINT}, protocol=${OTEL_EXPORTER_OTLP_PROTOCOL})"
 fi
 
 # Start the milter in background (MUST be running before Postfix starts).