--- a/client/js/tweetsource.js	Thu Feb 23 20:13:27 2012 +0100
+++ b/client/js/tweetsource.js	Fri Feb 24 11:22:59 2012 +0100
@@ -201,9 +201,10 @@
 }
 
 Btv_TweetSource.prototype.retrieveNewTweets = function() {
+    var _last = this.lastTweet();
     this.retrieveTweets({
         "pages": 1,
-        "since_id": this.lastTweet().id_str
+        "since_id": _last ? _last.id_str : 0
     });
 }