--- a/widget/src/xpwidgets/nsBaseWidget.cpp
+++ b/widget/src/xpwidgets/nsBaseWidget.cpp
@@ -291,17 +291,17 @@ nsIWidget* nsBaseWidget::GetParent(void)
 
 //-------------------------------------------------------------------------
 //
 // Get this nsBaseWidget top level widget
 //
 //-------------------------------------------------------------------------
 nsIWidget* nsBaseWidget::GetTopLevelWidget(PRInt32* aLevelsUp)
 {
-  nsIWidget *topLevelWidget, *widget = this;
+  nsIWidget *topLevelWidget = nsnull, *widget = this;
   if (aLevelsUp)
     *aLevelsUp = -1;
   while (widget) {
     topLevelWidget = widget;
     widget = widget->GetParent();
     if (aLevelsUp)
       ++*aLevelsUp;
   }