--- a/dom/media/MediaDecoder.h
+++ b/dom/media/MediaDecoder.h
@@ -377,19 +377,19 @@ private:
 
   void UpdateReadyState()
   {
     MOZ_ASSERT(NS_IsMainThread());
     MOZ_DIAGNOSTIC_ASSERT(!IsShutdown());
     GetOwner()->UpdateReadyState();
   }
 
-  virtual MediaDecoderOwner::NextFrameStatus NextFrameStatus()
+  MediaDecoderOwner::NextFrameStatus NextFrameStatus() const
   {
-    return !IsEnded() ? mNextFrameStatus : MediaDecoderOwner::NEXT_FRAME_UNAVAILABLE;
+    return mNextFrameStatus;
   }
 
   virtual MediaDecoderOwner::NextFrameStatus NextFrameBufferedStatus();
 
   // Returns a string describing the state of the media player internal
   // data. Used for debugging purposes.
   virtual void GetMozDebugReaderData(nsACString& aString);
 

--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -1942,16 +1942,20 @@ public:
       auto clockTime =
         std::max(mMaster->AudioEndTime(), mMaster->VideoEndTime());
       if (mMaster->mDuration.Ref()->IsInfinite()) {
         // We have a finite duration when playback reaches the end.
         mMaster->mDuration = Some(clockTime);
       }
       mMaster->UpdatePlaybackPosition(clockTime);
 
+      // Ensure readyState is updated before firing the 'ended' event.
+      mMaster->mOnNextFrameStatus.Notify(
+        MediaDecoderOwner::NEXT_FRAME_UNAVAILABLE);
+
       mMaster->mOnPlaybackEvent.Notify(MediaEventType::PlaybackEnded);
 
       mSentPlaybackEndedEvent = true;
 
       // MediaSink::GetEndTime() must be called before stopping playback.
       mMaster->StopMediaSink();
     }
   }