--- a/dom/media/TextTrack.cpp
+++ b/dom/media/TextTrack.cpp
@@ -131,16 +131,21 @@ TextTrack::GetId(nsAString& aId) const
   if (mTrackElement) {
     mTrackElement->GetAttribute(NS_LITERAL_STRING("id"), aId);
   }
 }
 
 void
 TextTrack::AddCue(TextTrackCue& aCue)
 {
+  TextTrack* oldTextTrack = aCue.GetTrack();
+  if (oldTextTrack) {
+    ErrorResult dummy;
+    oldTextTrack->RemoveCue(aCue, dummy);
+  }
   mCueList->AddCue(aCue);
   aCue.SetTrack(this);
   if (mTextTrackList) {
     HTMLMediaElement* mediaElement = mTextTrackList->GetMediaElement();
     if (mediaElement && (mMode != TextTrackMode::Disabled)) {
       mediaElement->NotifyCueAdded(aCue);
     }
   }