diff --git a/app/views/asciicasts/show.js.erb b/app/views/asciicasts/show.js.erb
index 7643b7c..7cd75b8 100644
--- a/app/views/asciicasts/show.js.erb
+++ b/app/views/asciicasts/show.js.erb
@@ -2,7 +2,7 @@
 
 (function() {
   function receiveSize(e) {
-    if (e.origin === document.location.protocol + "//<%= request.host %>") {
+    if (e.origin === document.location.protocol + "//<%= request.host_with_port %>") {
       var event = e.data[0];
       var data  = e.data[1];
       if (event == 'asciicast:size' && data.id == <%= @asciicast.id %>) {