diff --git a/CHANGES.md b/CHANGES.md
index 83b2dab691..59ff00980e 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -37,6 +37,7 @@
   requested at compile time (--enable with-js-error) or at startup (OCAMLRUNPARAM=b=1)
 * Runtime: allow dynlink of precompiled js with separate compilation (#1676)
 * Runtime: reimplement the runtime of weak and ephemeron (#1707)
+* Runtime: don't change the shape of mlbytes when converting to string
 * Lib: Modify Typed_array API for compatibility with WebAssembly
 * Lib: add details element and toggle event (#1728)
 * Toplevel: no longer set globals for toplevel initialization
diff --git a/runtime/js/mlBytes.js b/runtime/js/mlBytes.js
index 8566487548..2771ae23bd 100644
--- a/runtime/js/mlBytes.js
+++ b/runtime/js/mlBytes.js
@@ -703,10 +703,18 @@ function caml_string_lessthan(s1, s2) {
 
 //Provides: caml_string_of_bytes
 //Requires: caml_convert_string_to_bytes, caml_string_of_jsbytes
+//Requires: caml_subarray_to_jsbytes
 //If: js-string
 function caml_string_of_bytes(s) {
-  s.t & 6 && caml_convert_string_to_bytes(s);
-  return caml_string_of_jsbytes(s.c);
+  switch (s.t & 6) {
+    case 0 /* BYTES */:
+      return caml_string_of_jsbytes(s.c);
+    case 2 /* PARTIAL */:
+      caml_convert_string_to_bytes(s);
+      return caml_string_of_jsbytes(s.c);
+    case 4 /* ARRAY */:
+      return caml_subarray_to_jsbytes(s.c, 0, s.c.length);
+  }
 }
 
 //Provides: caml_bytes_of_string const