diff --git a/packages/js_of_ocaml/js_of_ocaml.3.10.0+flambda2/files/const_float_block.patch b/packages/js_of_ocaml/js_of_ocaml.3.10.0+flambda2/files/const_float_block.patch
new file mode 100644
index 0000000..402bb12
--- /dev/null
+++ b/packages/js_of_ocaml/js_of_ocaml.3.10.0+flambda2/files/const_float_block.patch
@@ -0,0 +1,14 @@
+diff --git a/compiler/lib/ocaml_compiler.ml b/compiler/lib/ocaml_compiler.ml
+index 29b6c8f058..93de84e68d 100644
+--- a/compiler/lib/ocaml_compiler.ml
++++ b/compiler/lib/ocaml_compiler.ml
+@@ -32,7 +32,7 @@ let rec constant_of_const : _ -> Code.constant =
+   | Const_base (Const_int64 i) -> Int64 i
+   | Const_base (Const_nativeint i) -> Int (Int32.of_nativeint_warning_on_overflow i)
+   | Const_immstring s -> String s
+-  | Const_float_array sl ->
++  | Const_float_array sl | Const_block_array sl ->
+       let l = List.map ~f:(fun f -> Code.Float (float_of_string f)) sl in
+       Tuple (Obj.double_array_tag, Array.of_list l, Unknown)
+   | ((Const_pointer (i, _)) [@if BUCKLESCRIPT]) ->
+
diff --git a/packages/js_of_ocaml/js_of_ocaml.3.10.0+flambda2/opam b/packages/js_of_ocaml/js_of_ocaml.3.10.0+flambda2/opam
new file mode 100644
index 0000000..c654c89
--- /dev/null
+++ b/packages/js_of_ocaml/js_of_ocaml.3.10.0+flambda2/opam
@@ -0,0 +1,40 @@
+opam-version: "2.0"
+name: "js_of_ocaml"
+version: "3.10.0"
+synopsis: "Compiler from OCaml bytecode to JavaScript"
+description:
+  "Js_of_ocaml is a compiler from OCaml bytecode to JavaScript. It makes it possible to run pure OCaml programs in JavaScript environment like browsers and Node.js"
+maintainer: "Ocsigen team <dev@ocsigen.org>"
+authors: "Ocsigen team <dev@ocsigen.org>"
+license:
+  "GPL-2.0-or-later AND LGPL-2.1-or-later WITH OCaml-LGPL-linking-exception"
+homepage: "https://ocsigen.github.io/js_of_ocaml"
+doc: "https://ocsigen.github.io/js_of_ocaml"
+bug-reports: "https://github.com/ocsigen/js_of_ocaml/issues"
+depends: [
+  "dune" {>= "2.8"}
+  "ocaml" {>= "4.04"}
+  "js_of_ocaml-compiler" {= version}
+  "ppxlib" {>= "0.15"}
+  "uchar"
+  "num" {with-test}
+  "ppx_expect" {with-test}
+  "re" {>= "1.9.0" & with-test}
+  "odoc" {with-doc}
+]
+build: [
+  ["dune" "subst"] {dev}
+  ["dune" "build" "-p" name "-j" jobs "@install" "@doc" {with-doc}]
+]
+dev-repo: "git+https://github.com/ocsigen/js_of_ocaml.git"
+url {
+  src:
+    "https://github.com/ocsigen/js_of_ocaml/releases/download/3.10.0/js_of_ocaml-3.10.0.tbz"
+  checksum: [
+    "sha256=7bfe95c283e30a53df9364555517aa4ea614876be566a86b33e6d0fefc4a6126"
+    "sha512=1815f0bfcea65a28082293756350a9365304584d3a19af0983e1498c6f8d7d25a751aec18560aa7b633b64b8adfb4417e9647cdf703bedcb7aaf316abf9a3243"
+  ]
+}
+x-commit-hash: "41ca9c4aa3004e11803c1e49d3ad77ec799bf853"
+patches: ["const_float_block.patch"]
+extra-files: [ ["const_float_block.patch" "md5=2d6cba3dddd007b57b6e5bc96a588100"] ]