diff --git a/calendar/inc/class.calendar_boupdate.inc.php b/calendar/inc/class.calendar_boupdate.inc.php
index 22fcb94fc2..998e46146f 100644
--- a/calendar/inc/class.calendar_boupdate.inc.php
+++ b/calendar/inc/class.calendar_boupdate.inc.php
@@ -330,7 +330,7 @@ class calendar_boupdate extends calendar_bo
 			{
 				foreach($conflicts as $key => $conflict)
 				{
-					$conflict['participants'] = array_intersect_key($conflict['participants'],$event['participants']);
+						$conflict['participants'] = array_intersect_key((array)$conflict['participants'],$event['participants']);
 					if (!$this->check_perms(EGW_ACL_READ,$conflict))
 					{
 						$conflicts[$key] = array(
diff --git a/calendar/inc/class.calendar_uiforms.inc.php b/calendar/inc/class.calendar_uiforms.inc.php
index de857895f1..04808bd27c 100644
--- a/calendar/inc/class.calendar_uiforms.inc.php
+++ b/calendar/inc/class.calendar_uiforms.inc.php
@@ -1791,13 +1791,13 @@ class calendar_uiforms extends calendar_ui
 				'tooltip_participants' => $is_readable ? implode(', ',$this->bo->participants($conflict)) : '',
 				'time' => $this->bo->long_date($conflict['start'],$conflict['end'],true),
 				'conflicting_participants' => implode(",\n",$this->bo->participants(array(
-					'participants' => array_intersect_key($conflict['participants'],$event['participants']),
+					'participants' => array_intersect_key((array)$conflict['participants'],$event['participants']),
 				),true,true)),	// show group invitations too
 				'icon_recur' => $conflict['recur_type'] != MCAL_RECUR_NONE ? 'recur' : '',
 				'text_recur' => $conflict['recur_type'] != MCAL_RECUR_NONE ? lang('Recurring event') : ' ',
 			);
-			$allConflicts += array_intersect_key($conflict['participants'],$event['participants']);
-		}
+				$allConflicts += array_intersect_key((array)$conflict['participants'],$event['participants']);
+			}
 		$content = $event + array(
 			'conflicts' => array_values($conflicts),	// conflicts have id-start as key
 		);