diff --git a/dom/src/base/nsDOMClassInfo.cpp b/dom/src/base/nsDOMClassInfo.cpp
index fa9dd20a189a..20d3113cb0a7 100644
--- a/dom/src/base/nsDOMClassInfo.cpp
+++ b/dom/src/base/nsDOMClassInfo.cpp
@@ -4662,11 +4662,29 @@ nsWindowSH::AddProperty(nsIXPConnectWrappedNative *wrapper, JSContext *cx,
       printf(" --- Forwarding add to inner window %p\n", (void *)innerWin);
 #endif
 
-      // Forward the add to the inner object
       jsid interned_id;
-      *_retval = (::JS_ValueToId(cx, id, &interned_id) &&
-                  OBJ_DEFINE_PROPERTY(cx, innerObj, interned_id, *vp, nsnull,
-                                      nsnull, JSPROP_ENUMERATE, nsnull));
+      if (!::JS_ValueToId(cx, id, &interned_id)) {
+        *_retval = JS_FALSE;
+        return NS_OK;
+      }
+
+      JSProperty *prop = nsnull;
+      JSObject *pobj;
+      if (!OBJ_LOOKUP_PROPERTY(cx, obj, interned_id, &pobj, &prop)) {
+        *_retval = JS_FALSE;
+        return NS_OK;
+      }
+
+      NS_ASSERTION(prop && obj == pobj, "The JS engine lies");
+      JSScopeProperty *sprop = reinterpret_cast<JSScopeProperty *>(prop);
+      JSPropertyOp getter = sprop->getter;
+      JSPropertyOp setter = sprop->setter;
+      uintN attrs = sprop->attrs;
+      OBJ_DROP_PROPERTY(cx, pobj, prop);
+
+      // Forward the add to the inner object
+      *_retval = OBJ_DEFINE_PROPERTY(cx, innerObj, interned_id, *vp, getter,
+                                     setter, attrs | JSPROP_ENUMERATE, nsnull);
 
       return NS_OK;
     }