--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -4702,17 +4702,19 @@ HTMLMediaElement::UpdateReadyStateIntern
     }
     if (hasVideoTracks) {
       mediaInfo.EnableVideo();
     }
     MetadataLoaded(&mediaInfo, nsAutoPtr<const MetadataTags>(nullptr));
   }
 
   enum NextFrameStatus nextFrameStatus = NextFrameStatus();
-  if (nextFrameStatus == NEXT_FRAME_UNAVAILABLE) {
+  if (nextFrameStatus == NEXT_FRAME_UNAVAILABLE ||
+      (nextFrameStatus == NEXT_FRAME_UNAVAILABLE_BUFFERING &&
+       mWaitingForKey == WAITING_FOR_KEY)) {
     if (mWaitingForKey != NOT_WAITING_FOR_KEY) {
       // http://w3c.github.io/encrypted-media/#wait-for-key
       // Continuing 7.3.4 Queue a "waitingforkey" Event
       // 4. Queue a task to fire a simple event named waitingforkey
       // at the media element.
       if (mWaitingForKey == WAITING_FOR_KEY) {
         mWaitingForKey = WAITING_FOR_KEY_DISPATCHED;
         DispatchAsyncEvent(NS_LITERAL_STRING("waitingforkey"));