diff --git a/dom/src/base/nsDOMWindowList.cpp b/dom/src/base/nsDOMWindowList.cpp
index d44f69e5e88f..c3c8cb76ee44 100644
--- a/dom/src/base/nsDOMWindowList.cpp
+++ b/dom/src/base/nsDOMWindowList.cpp
@@ -116,7 +116,8 @@ nsDOMWindowList::NamedItem(const nsString& aName, nsIDOMWindow** aReturn)
   mWebShell->FindChildWithName(aName.GetUnicode(), *getter_AddRefs(item));
 
   nsCOMPtr<nsIScriptGlobalObject> globalObject(do_GetInterface(item));
-  if (NS_WARN_IF_FALSE(globalObject, "Couldn't get to the globalObject")) {
+  NS_ASSERTION(globalObject != nsnull, "Couldn't get to the globalObject");
+  if (globalObject) {
     CallQueryInterface(globalObject.get(), aReturn);
   }
   else {