diff --git a/uriloader/exthandler/nsExternalHelperAppService.cpp b/uriloader/exthandler/nsExternalHelperAppService.cpp
index 4326dac79c5c..0a4bb5f78159 100644
--- a/uriloader/exthandler/nsExternalHelperAppService.cpp
+++ b/uriloader/exthandler/nsExternalHelperAppService.cpp
@@ -625,7 +625,7 @@ nsresult nsExternalAppHandler::PromptForSaveToFile(nsILocalFile ** aNewFile, con
   nsCOMPtr<nsIHelperAppLauncherDialog> dlgService( do_GetService( NS_IHELPERAPPLAUNCHERDLG_PROGID ) );
   nsresult rv = NS_OK;
   if ( dlgService ) 
-    rv = dlgService->PromptForSaveToFile(mWindowContext, aDefaultFile, NS_ConvertASCIItoUCS2(mTempFileExtension), aNewFile);
+    rv = dlgService->PromptForSaveToFile(mWindowContext, aDefaultFile, NS_ConvertASCIItoUCS2(mTempFileExtension).get(), aNewFile);
 
   return rv;
 }