diff --git a/calendar/inc/class.calendar_so.inc.php b/calendar/inc/class.calendar_so.inc.php
index 6b956b082b..aca679c91e 100644
--- a/calendar/inc/class.calendar_so.inc.php
+++ b/calendar/inc/class.calendar_so.inc.php
@@ -493,7 +493,10 @@ class calendar_so
 					if ($type == 'u' && $filter == 'owner')
 					{
 						$cal_table_def = $this->db->get_table_definitions('calendar',$this->cal_table);
-						$owner_or = $this->db->expression($cal_table_def,array('cal_owner' => $ids));
+						// only users can be owners, no need to add groups
+						$user_ids = array();
+						foreach($ids as $user_id) if ($GLOBALS['egw']->accounts->get_type($user_id) === 'u') $user_ids[] = $user_id;
+						$owner_or = $this->db->expression($cal_table_def,array('cal_owner' => $user_ids));
 					}
 				}
 				else