diff --git a/mozilla/js/rhino/src/org/mozilla/javascript/NativeIterator.java b/mozilla/js/rhino/src/org/mozilla/javascript/NativeIterator.java
index 64544fff616..1e72be7989f 100644
--- a/mozilla/js/rhino/src/org/mozilla/javascript/NativeIterator.java
+++ b/mozilla/js/rhino/src/org/mozilla/javascript/NativeIterator.java
@@ -163,8 +163,9 @@ public final class NativeIterator extends IdScriptableObject {
         if (args.length == 0 || args[0] == null || 
             args[0] == Undefined.instance)
         {
+            Object argument = args.length == 0 ? Undefined.instance : args[0];
             throw ScriptRuntime.typeError1("msg.no.properties", 
-                                           ScriptRuntime.toString(args[0]));
+                                           ScriptRuntime.toString(argument));
         }
         Scriptable obj = ScriptRuntime.toObject(scope, args[0]);
         boolean keyOnly = args.length > 1 && ScriptRuntime.toBoolean(args[1]);