ReferenceError: "twttr is not defined" even while using twttr.ready()

Firebug console throws an error. It states that the code which I'm trying to use for tracking social events is used before //platform.twitter.com/widgets.js has finished loading asynchronously.

ReferenceError: twttr is not defined twttr.ready(function (twttr) {

However, I followed Twitter documentation ( http://ift.tt/1FjKDZz ), and wrapped it around twttr.ready(), in the same way one does with Facebook events.

<script type="text/javascript">
    window.fbAsyncInit = function() {
          FB.Event.subscribe('edge.create', function(targetUrl) {
          ga('send', 'social', 'facebook', 'like', targetUrl);
        });
          FB.Event.subscribe('edge.remove', function(targetUrl) {
          ga('send', 'social', 'facebook', 'unlike', targetUrl);
        });
    }
    twttr.ready(function (twttr) {
     twttr.events.bind('tweet', function(e){
      if(!e) return;
      ga('send', 'social', 'twitter', 'tweet', theURL);
     })
    });
</script>

Any hints?