diff --git a/lib/webrtc/call.js b/lib/webrtc/call.js
index 5ec072761..84edace08 100644
--- a/lib/webrtc/call.js
+++ b/lib/webrtc/call.js
@@ -156,7 +156,11 @@ MatrixCall.prototype._initWithInvite = function(event) {
     // firefox and OpenWebRTC's RTCPeerConnection doesn't add streams until it
     // starts getting media on them so we need to figure out whether a video
     // channel has been offered by ourselves.
-    if (this.msg.offer.sdp.indexOf('m=video') > -1) {
+    if (
+        this.msg.offer &&
+        this.msg.offer.sdp &&
+        this.msg.offer.sdp.indexOf('m=video') > -1
+    ) {
         this.type = 'video';
     }
     else {