diff --git a/src/util/websocket/browser_websocket.js b/src/util/websocket/browser_websocket.js
index c7e525f0..9a7de8ce 100644
--- a/src/util/websocket/browser_websocket.js
+++ b/src/util/websocket/browser_websocket.js
@@ -4,6 +4,7 @@ var WS = global.MozWebSocket || global.WebSocket;
 
 module.exports = {
   create: function(url, protocols, options) {
+    if (typeof WS !== 'function') return null;
     return new WS(url);
   }
 };