diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index 53fa00a0..a24f3539 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -1975,8 +1975,8 @@ class calendar extends rcube_plugin
   private function write_preprocess(&$event, $action)
   {
     // convert dates into DateTime objects in user's current timezone
-    $event['start'] = new DateTime($event['start'], $this->timezone);
-    $event['end'] = new DateTime($event['end'], $this->timezone);
+    $event['start']  = new DateTime($event['start'], $this->timezone);
+    $event['end']    = new DateTime($event['end'], $this->timezone);
     $event['allday'] = (bool)$event['allday'];
 
     // start/end is all we need for 'move' action (#1480)
@@ -2026,7 +2026,7 @@ class calendar extends rcube_plugin
       foreach ((array)$event['attendees'] as $i => $attendee) {
         if ($attendee['role'] == 'ORGANIZER')
           $organizer = $i;
-        if ($attendee['email'] == in_array(strtolower($attendee['email']), $emails))
+        if ($attendee['email'] && in_array(strtolower($attendee['email']), $emails))
           $owner = $i;
         if (!isset($attendee['rsvp']))
           $event['attendees'][$i]['rsvp'] = true;
diff --git a/plugins/calendar/drivers/kolab/kolab_calendar.php b/plugins/calendar/drivers/kolab/kolab_calendar.php
index 107a764c..fe2ede53 100644
--- a/plugins/calendar/drivers/kolab/kolab_calendar.php
+++ b/plugins/calendar/drivers/kolab/kolab_calendar.php
@@ -763,11 +763,25 @@ class kolab_calendar extends kolab_storage_folder_api
   private function _from_driver_event($event, $old = array())
   {
     // set current user as ORGANIZER
-    $identity = $this->cal->rc->user->list_emails(true);
-    if (empty($event['attendees']) && $identity['email'])
-      $event['attendees'] = array(array('role' => 'ORGANIZER', 'name' => $identity['name'], 'email' => $identity['email']));
+    if ($identity = $this->cal->rc->user->list_emails(true)) {
+      $event['attendees'] = (array) $event['attendees'];
+      $found = false;
 
-    $event['_owner'] = $identity['email'];
+      // there can be only resources on attendees list (T1484)
+      // let's check the existence of an organizer
+      foreach ($event['attendees'] as $attendee) {
+        if ($attendee['role'] == 'ORGANIZER') {
+          $found = true;
+          break;
+        }
+      }
+
+      if (!$found) {
+        $event['attendees'][] = array('role' => 'ORGANIZER', 'name' => $identity['name'], 'email' => $identity['email']);
+      }
+
+      $event['_owner'] = $identity['email'];
+    }
 
     // remove EXDATE values if RDATE is given
     if (!empty($event['recurrence']['RDATE'])) {
@@ -792,7 +806,6 @@ class kolab_calendar extends kolab_storage_folder_api
       });
     }
 
-
     // remove some internal properties which should not be saved
     unset($event['_savemode'], $event['_fromcalendar'], $event['_identity'], $event['_folder_id'],
       $event['recurrence_id'], $event['attachments'], $event['deleted_attachments'], $event['className']);