diff --git a/plugins/calendar/drivers/kolab/kolab_driver.php b/plugins/calendar/drivers/kolab/kolab_driver.php
index fed7aed5..0eafc3bd 100644
--- a/plugins/calendar/drivers/kolab/kolab_driver.php
+++ b/plugins/calendar/drivers/kolab/kolab_driver.php
@@ -346,13 +346,16 @@ class kolab_driver extends calendar_driver
     $this->_read_calendars();
 
     // create calendar object if necesary
-    if (!$this->calendars[$id] && in_array($id, array(self::INVITATIONS_CALENDAR_PENDING, self::INVITATIONS_CALENDAR_DECLINED))) {
-      $this->calendars[$id] = new kolab_invitation_calendar($id, $this->cal);
-    }
-    else if (!$this->calendars[$id] && $id !== self::BIRTHDAY_CALENDAR_ID) {
-      $calendar = kolab_calendar::factory($id, $this->cal);
-      if ($calendar->ready)
-        $this->calendars[$calendar->id] = $calendar;
+    if (!$this->calendars[$id]) {
+      if (in_array($id, array(self::INVITATIONS_CALENDAR_PENDING, self::INVITATIONS_CALENDAR_DECLINED))) {
+        $this->calendars[$id] = new kolab_invitation_calendar($id, $this->cal);
+      }
+      else if ($id !== self::BIRTHDAY_CALENDAR_ID) {
+        $calendar = kolab_calendar::factory($id, $this->cal);
+        if ($calendar->ready) {
+          $this->calendars[$calendar->id] = $calendar;
+        }
+      }
     }
 
     return $this->calendars[$id];
diff --git a/plugins/calendar/drivers/kolab/kolab_invitation_calendar.php b/plugins/calendar/drivers/kolab/kolab_invitation_calendar.php
index 5e81377b..b41e2964 100644
--- a/plugins/calendar/drivers/kolab/kolab_invitation_calendar.php
+++ b/plugins/calendar/drivers/kolab/kolab_invitation_calendar.php
@@ -197,7 +197,7 @@ class kolab_invitation_calendar
     else {
       $cal = null;
       foreach (kolab_storage::list_folders('', '*', 'event', null) as $foldername) {
-        $cal = new kolab_calendar($foldername, $this->cal);
+        $cal = $this->_get_calendar($foldername);
         if ($cal->ready && $cal->storage && $cal->get_event($event['id'])) {
           break;
         }
@@ -233,7 +233,7 @@ class kolab_invitation_calendar
     // aggregate events from all calendar folders
     $events = array();
     foreach (kolab_storage::list_folders('', '*', 'event', null) as $foldername) {
-      $cal = new kolab_calendar($foldername, $this->cal);
+      $cal = $this->_get_calendar($foldername);
       if ($cal->get_namespace() == 'other')
         continue;
 
@@ -287,7 +287,7 @@ class kolab_invitation_calendar
     // aggregate counts from all calendar folders
     $count = 0;
     foreach (kolab_storage::list_folders('', '*', 'event', null) as $foldername) {
-      $cal = new kolab_calendar($foldername, $this->cal);
+      $cal = $this->_get_calendar($foldername);
       if ($cal->get_namespace() == 'other')
         continue;
 
@@ -297,6 +297,15 @@ class kolab_invitation_calendar
     return $count;
   }
 
+  /**
+   * Get calendar object instance (that maybe already initialized)
+   */
+  private function _get_calendar($folder_name)
+  {
+    $id = kolab_storage::folder_id($folder_name, true);
+    return $this->cal->driver->get_calendar($id);
+  }
+
   /**
    * Helper method to modify some event properties
    */