--- a/dom/media/PeerConnection.js
+++ b/dom/media/PeerConnection.js
@@ -1277,16 +1277,17 @@ class RTCPeerConnection {
     return {
       sources: cache.rtpSourcesByTrackId[id],
       sourceClockOffset: cache.timestampOffset,
       jsTimestamp: cache.jsTimestamp,
     };
   }
 
   addTransceiver(sendTrackOrKind, init) {
+    this._checkClosed();
     let transceiver = this._addTransceiverNoEvents(sendTrackOrKind, init);
     this.updateNegotiationNeeded();
     return transceiver;
   }
 
   _syncTransceivers() {
     this._transceivers.forEach(transceiver => transceiver.sync());
   }