--- a/widget/nsGUIEventIPC.h
+++ b/widget/nsGUIEventIPC.h
@@ -260,17 +260,17 @@ struct ParamTraits<mozilla::WidgetPointe
 template<>
 struct ParamTraits<mozilla::WidgetMouseEvent>
 {
   typedef mozilla::WidgetMouseEvent paramType;
 
   static void Write(Message* aMsg, const paramType& aParam)
   {
     WriteParam(aMsg, static_cast<const mozilla::WidgetMouseEventBase&>(aParam));
-    WriteParam(aMsg, static_cast<mozilla::WidgetPointerHelper>(aParam));
+    WriteParam(aMsg, static_cast<const mozilla::WidgetPointerHelper&>(aParam));
     WriteParam(aMsg, aParam.mIgnoreRootScrollFrame);
     WriteParam(aMsg, static_cast<paramType::ReasonType>(aParam.mReason));
     WriteParam(aMsg, static_cast<paramType::ContextMenuTriggerType>(
                        aParam.mContextMenuTrigger));
     WriteParam(aMsg, static_cast<paramType::ExitFromType>(aParam.mExitFrom));
     WriteParam(aMsg, aParam.mClickCount);
   }