diff --git a/lib/action.php b/lib/action.php
index cc4f4aad07..0a607b42d5 100644
--- a/lib/action.php
+++ b/lib/action.php
@@ -974,7 +974,7 @@ class Action extends HTMLOutputter // lawsuit
 
         if (is_null($arg)) {
             return $def;
-        } else if (in_array($arg, array('true', 'yes', '1'))) {
+        } else if (in_array($arg, array('true', 'yes', '1', 'on'))) {
             return true;
         } else if (in_array($arg, array('false', 'no', '0'))) {
             return false;