diff --git a/app/controllers/topics_controller.rb b/app/controllers/topics_controller.rb
index d226f6f1c8f..8e4f1c12cd8 100644
--- a/app/controllers/topics_controller.rb
+++ b/app/controllers/topics_controller.rb
@@ -40,7 +40,9 @@ class TopicsController < ApplicationController
   end
 
   def show
-    flash["referer"] ||= request.referer
+    if request.referer
+      flash["referer"] ||= request.referer[0..255]
+    end
 
     # We'd like to migrate the wordpress feed to another url. This keeps up backwards compatibility with
     # existing installs.