--- a/dom/media/WebVTTListener.cpp
+++ b/dom/media/WebVTTListener.cpp
@@ -155,17 +155,17 @@ WebVTTListener::OnDataAvailable(nsIReque
 
 NS_IMETHODIMP
 WebVTTListener::OnCue(JS::Handle<JS::Value> aCue, JSContext* aCx)
 {
   if (!aCue.isObject()) {
     return NS_ERROR_FAILURE;
   }
 
-  TextTrackCue* cue;
+  TextTrackCue* cue = nullptr;
   nsresult rv = UNWRAP_OBJECT(VTTCue, &aCue.toObject(), cue);
   NS_ENSURE_SUCCESS(rv, rv);
 
   cue->SetTrackElement(mElement);
   mElement->mTrack->AddCue(*cue);
 
   return NS_OK;
 }