diff --git a/src/webrtc/call.js b/src/webrtc/call.js
index 1ad12c8d2..f730a2067 100644
--- a/src/webrtc/call.js
+++ b/src/webrtc/call.js
@@ -516,8 +516,10 @@ MatrixCall.prototype._gotUserMediaForInvite = function(stream) {
         }, 0);
     }
 
-    this.screenSharingStream.addTrack(stream.getAudioTracks()[0]);
-    stream = this.screenSharingStream;
+    if (this.screenSharingStream) {
+        this.screenSharingStream.addTrack(stream.getAudioTracks()[0]);
+        stream = this.screenSharingStream;
+    }
 
     this.localAVStream = stream;
     // why do we enable audio (and only audio) tracks here? -- matthew