--- a/dom/media/MediaDecoder.cpp
+++ b/dom/media/MediaDecoder.cpp
@@ -1034,19 +1034,17 @@ MediaDecoder::ResetConnectionState()
   // to play the Rtsp streaming next time.
   Shutdown();
 }
 
 void
 MediaDecoder::NetworkError()
 {
   MOZ_ASSERT(NS_IsMainThread());
-  if (IsShutdown())
-    return;
-
+  MOZ_ASSERT(!IsShutdown());
   mOwner->NetworkError();
   Shutdown();
 }
 
 void
 MediaDecoder::DecodeError()
 {
   MOZ_ASSERT(NS_IsMainThread());