diff --git a/mozilla/modules/plugin/base/src/nsPluginViewer.cpp b/mozilla/modules/plugin/base/src/nsPluginViewer.cpp
index b5ea2bd084b..48720dc4219 100644
--- a/mozilla/modules/plugin/base/src/nsPluginViewer.cpp
+++ b/mozilla/modules/plugin/base/src/nsPluginViewer.cpp
@@ -1183,7 +1183,7 @@ void pluginInstanceOwner::GUItoMacEvent(const nsGUIEvent& anEvent, EventRecord&
 nsEventStatus pluginInstanceOwner::ProcessEvent(const nsGUIEvent& anEvent)
 {
   nsEventStatus rv = nsEventStatus_eIgnore;
-  if (!mInstance)   // if mInstance is null, we shouldn't be here
+  if (!mInstance || !mWindow)   // if the instance or the window is null, we shouldn't be here
     return rv;
 
 #ifdef XP_MAC