diff --git a/mozilla/webshell/tests/viewer/nsViewerApp.cpp b/mozilla/webshell/tests/viewer/nsViewerApp.cpp
index f5bdc62b2b2..b27f24dbae6 100644
--- a/mozilla/webshell/tests/viewer/nsViewerApp.cpp
+++ b/mozilla/webshell/tests/viewer/nsViewerApp.cpp
@@ -115,7 +115,8 @@ nsViewerApp::QueryInterface(REFNSIID aIID, void** aInstancePtrResult)
     return NS_ERROR_NULL_POINTER;
   }
   if (aIID.Equals(kISupportsIID)) {
-    *aInstancePtrResult = (void*) ((nsISupports*)((nsIBrowserWindow*)this));
+    nsISupports* tmp = this;
+    *aInstancePtrResult = (void*) tmp;
     NS_ADDREF_THIS();
     return NS_OK;
   }