diff --git a/guides/source/action_controller_overview.textile b/guides/source/action_controller_overview.textile
index d6f39c486d..a76a116103 100644
--- a/guides/source/action_controller_overview.textile
+++ b/guides/source/action_controller_overview.textile
@@ -152,6 +152,7 @@ You can set global default parameters that will be used when generating URLs wit
 
 <ruby>
 class ApplicationController < ActionController::Base
+  # This method must return a hash with symbolized keys.
   def default_url_options
     {:locale => I18n.locale}
   end