diff --git a/runtime/js/jslib.js b/runtime/js/jslib.js
index da4db1a2bb..03fbdbefe9 100644
--- a/runtime/js/jslib.js
+++ b/runtime/js/jslib.js
@@ -416,7 +416,8 @@ function caml_js_wrap_callback_unsafe(f) {
 //Requires: caml_callback, caml_js_wrap_callback
 function caml_js_wrap_meth_callback(f) {
   return function (...args) {
-    var res = caml_callback(f, [this, ...args]);
+    args.unshift(this);
+    var res = caml_callback(f, args);
     return res instanceof Function ? caml_js_wrap_callback(res) : res;
   };
 }
@@ -431,8 +432,8 @@ function caml_js_wrap_meth_callback_arguments(f) {
 //Requires: caml_callback
 function caml_js_wrap_meth_callback_strict(arity, f) {
   return function (...args) {
-    args = [this, ...args];
-    args.length = arity + 1;
+    args.length = arity;
+    args.unshift(this);
     return caml_callback(f, args);
   };
 }
@@ -441,7 +442,7 @@ function caml_js_wrap_meth_callback_strict(arity, f) {
 function caml_js_wrap_meth_callback_unsafe(f) {
   return function (...args) {
     var len = caml_js_function_arity(f);
-    args = [this, ...args];
+    args.unshift(this);
     args.length = len;
     return caml_callback(f, args);
   };
diff --git a/runtime/js/stdlib.js b/runtime/js/stdlib.js
index cd33308551..307986787d 100644
--- a/runtime/js/stdlib.js
+++ b/runtime/js/stdlib.js
@@ -53,7 +53,7 @@ function caml_call_gen(f, args) {
       default: {
         var g = function (...extra_args) {
           if (extra_args.length === 0) extra_args = [undefined];
-          return caml_call_gen(f, [...args, ...extra_args]);
+          return caml_call_gen(f, args.concat(extra_args));
         };
       }
     }
@@ -111,7 +111,7 @@ function caml_call_gen(f, args) {
         args.length = argsLen;
         var g = function (...extra_args) {
           if (extra_args.length === 0) extra_args = [undefined];
-          return caml_call_gen(f, [...args, ...extra_args]);
+          return caml_call_gen(f, args.concat(extra_args));
         };
       }
     }
diff --git a/runtime/js/stdlib_modern.js b/runtime/js/stdlib_modern.js
index 82ca3c7fee..88c4806a1f 100644
--- a/runtime/js/stdlib_modern.js
+++ b/runtime/js/stdlib_modern.js
@@ -51,7 +51,7 @@ function caml_call_gen(f, args) {
       default: {
         var g = function (...extra_args) {
           if (extra_args.length === 0) extra_args = [undefined];
-          return caml_call_gen(f, [...args, ...extra_args]);
+          return caml_call_gen(f, args.concat(extra_args));
         };
       }
     }
@@ -107,7 +107,7 @@ function caml_call_gen(f, args) {
         args.length = argsLen;
         var g = function (...extra_args) {
           if (extra_args.length === 0) extra_args = [undefined];
-          return caml_call_gen(f, [...args, ...extra_args]);
+          return caml_call_gen(f, args.concat(extra_args));
         };
       }
     }