diff --git a/src/js/json.js b/src/js/json.js
index 73d7802..c6dbed9 100644
--- a/src/js/json.js
+++ b/src/js/json.js
@@ -19,6 +19,10 @@
 var MaxSimple;
 var MinSimple;
 var ObjectHasOwnProperty;
+var Stack;
+var StackHas;
+var StackPop;
+var StackPush;
 var toStringTagSymbol = utils.ImportNow("to_string_tag_symbol");
 
 utils.Import(function(from) {
@@ -26,6 +30,10 @@
   MaxSimple = from.MaxSimple;
   MinSimple = from.MinSimple;
   ObjectHasOwnProperty = from.ObjectHasOwnProperty;
+  Stack = from.Stack;
+  StackHas = from.StackHas;
+  StackPop = from.StackPop;
+  StackPush = from.StackPush;
 });
 
 // -------------------------------------------------------------------
@@ -51,7 +59,9 @@
         }
       }
     } else {
-      for (var p of %object_keys(val)) {
+      var keys = %object_keys(val);
+      for (var i = 0; i < keys.length; i++) {
+        var p = keys[i];
         var newElement = InternalizeJSONProperty(val, p, reviver);
         if (IS_UNDEFINED(newElement)) {
           %reflect_delete_property(val, p);
@@ -76,7 +86,8 @@
 
 
 function SerializeArray(value, replacer, stack, indent, gap) {
-  if (!%PushIfAbsent(stack, value)) throw MakeTypeError(kCircularStructure);
+  if (StackHas(stack, value)) throw MakeTypeError(kCircularStructure);
+  StackPush(stack, value);
   var stepback = indent;
   indent += gap;
   var partial = new InternalArray();
@@ -99,13 +110,14 @@
   } else {
     final = "[]";
   }
-  stack.pop();
+  StackPop(stack);
   return final;
 }
 
 
 function SerializeObject(value, replacer, stack, indent, gap) {
-  if (!%PushIfAbsent(stack, value)) throw MakeTypeError(kCircularStructure);
+  if (StackHas(stack, value)) throw MakeTypeError(kCircularStructure);
+  StackPush(stack, value);
   var stepback = indent;
   indent += gap;
   var partial = new InternalArray();
@@ -122,7 +134,9 @@
       }
     }
   } else {
-    for (var p of %object_keys(value)) {
+    var keys = %object_keys(value);
+    for (var i = 0; i < keys.length; i++) {
+      var p = keys[i];
       var strP = JSONSerialize(p, value, replacer, stack, indent, gap);
       if (!IS_UNDEFINED(strP)) {
         var member = %QuoteJSONString(p) + ":";
@@ -142,7 +156,7 @@
   } else {
     final = "{}";
   }
-  stack.pop();
+  StackPop(stack);
   return final;
 }
 
@@ -237,7 +251,7 @@
   if (!IS_CALLABLE(replacer) && !property_list && !gap && !IS_PROXY(value)) {
     return %BasicJSONStringify(value);
   }
-  return JSONSerialize('', {'': value}, replacer, new InternalArray(), "", gap);
+  return JSONSerialize('', {'': value}, replacer, new Stack(), "", gap);
 }
 
 // -------------------------------------------------------------------
@@ -275,7 +289,7 @@
   var holder = {};
   holder[key] = object;
   // No need to pass the actual holder since there is no replacer function.
-  return JSONSerialize(key, holder, UNDEFINED, new InternalArray(), "", "");
+  return JSONSerialize(key, holder, UNDEFINED, new Stack(), "", "");
 }
 
 %InstallToContext(["json_serialize_adapter", JsonSerializeAdapter]);