--- contrib/activityhistory/activityhistory.module.orig	2009-01-20 18:43:03.000000000 +0100
+++ contrib/activityhistory/activityhistory.module	2009-03-23 09:43:42.000000000 +0100
@@ -21,7 +21,7 @@ function activityhistory_activityapi(&$a
       $activity['activity_history_new'] = $history[$activity['aid']][$user->uid];
 
       if ($activity['activity_history_new']) {
-        if ($activity['mark']) {
+        if (isset($activity['mark']) && $activity['mark']) {
           $activity['mark'] .= ' '. $activity['activity_history_new'] .' ';
         }
         else {