diff --git a/CHANGES.md b/CHANGES.md
index 64da495910..b594e10d8a 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -9,6 +9,7 @@
 * Compiler: reduce memory consumption when parsing js
 * Compiler: parsing js can return a list of token, the list was sometime incorrect
 * Sourcemap: stop producing sourcemaps mappings with negative lines or columns
+* Runtime: fix marshalling with sharing and string (use-js-string)
 
 # 5.1.1 (2023-03-15) - Lille
 ## Bug fixes
diff --git a/compiler/tests-jsoo/test_marshal.ml b/compiler/tests-jsoo/test_marshal.ml
index f0fd7330d4..734f0c2145 100644
--- a/compiler/tests-jsoo/test_marshal.ml
+++ b/compiler/tests-jsoo/test_marshal.ml
@@ -154,3 +154,14 @@ let%expect_test _ =
   in
   Printf.printf "%s ... (%d)\n" (String.sub s 0 20) (String.length s);
   [%expect {| cccccccccccccccccccc ... (10000) |}]
+
+let%expect_test "test sharing of string" =
+  let s = "AString" in
+  let p = s, s in
+  let obj = [ p; p ] in
+  Printf.printf "%S" (Marshal.to_string s []);
+  [%expect
+    {| "\132\149\166\190\000\000\000\b\000\000\000\001\000\000\000\003\000\000\000\002'AString" |}];
+  Printf.printf "%S" (Marshal.to_string obj []);
+  [%expect
+    {| "\132\149\166\190\000\000\000\016\000\000\000\004\000\000\000\012\000\000\000\011\160\160'AString\004\001\160\004\003@" |}]
diff --git a/runtime/marshal.js b/runtime/marshal.js
index 9c5bb6eb22..9fe2d6c4d9 100644
--- a/runtime/marshal.js
+++ b/runtime/marshal.js
@@ -552,7 +552,7 @@ function caml_marshal_data_size (s, ofs) {
 
 //Provides: MlObjectTable
 var MlObjectTable;
-if (typeof globalThis.WeakMap === 'undefined') {
+if (typeof globalThis.Map === 'undefined') {
   MlObjectTable = function() {
     /* polyfill (using linear search) */
     function NaiveLookup(objs) { this.objs = objs; }
@@ -572,7 +572,7 @@ if (typeof globalThis.WeakMap === 'undefined') {
 }
 else {
   MlObjectTable = function MlObjectTable() {
-    this.objs = []; this.lookup = new globalThis.WeakMap();
+    this.objs = []; this.lookup = new globalThis.Map();
   };
 }
 
@@ -715,6 +715,7 @@ var caml_output_val = function (){
         writer.size_32 += 1 + (((len + 4) / 4)|0);
         writer.size_64 += 1 + (((len + 8) / 8)|0);
       } else if (caml_is_ml_string(v)) {
+        if (memo(v)) return;
         var len = caml_ml_string_length(v);
         if (len < 0x20)
           writer.write (8, 0x20 /*cst.PREFIX_SMALL_STRING*/ + len);