diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index fc4bbfff..f5c2c043 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -978,7 +978,8 @@ class calendar extends rcube_plugin
 
       case "rsvp":
         $itip_sending  = $this->rc->config->get('calendar_itip_send_option', $this->defaults['calendar_itip_send_option']);
-        $status        = rcube_utils::get_input_value('status', rcube_utils::INPUT_GPC);
+        $status        = rcube_utils::get_input_value('status', rcube_utils::INPUT_POST);
+        $attendees     = rcube_utils::get_input_value('attendees', rcube_utils::INPUT_POST);
         $reply_comment = $event['comment'];
 
         $this->write_preprocess($event, 'edit');
@@ -990,7 +991,7 @@ class calendar extends rcube_plugin
         // send invitation to delegatee + add it as attendee
         if ($status == 'delegated' && $event['to']) {
           $itip = $this->load_itip();
-          if ($itip->delegate_to($ev, $event['to'], (bool)$event['rsvp'])) {
+          if ($itip->delegate_to($ev, $event['to'], (bool)$event['rsvp'], $attendees)) {
             $this->rc->output->show_message('calendar.itipsendsuccess', 'confirmation');
             $noreply = false;
           }
@@ -998,7 +999,12 @@ class calendar extends rcube_plugin
 
         $event = $ev;
 
-        if ($success = $this->driver->edit_rsvp($event, $status)) {
+        // compose a list of attendees affected by this change
+        $updated_attendees = array_filter(array_map(function($j) use ($ev) {
+          return $ev['attendees'][$j];
+        }, $attendees));
+
+        if ($success = $this->driver->edit_rsvp($event, $status, $updated_attendees)) {
           $noreply = rcube_utils::get_input_value('noreply', rcube_utils::INPUT_GPC);
           $noreply = intval($noreply) || $status == 'needs-action' || $itip_sending === 0;
           $reload  = $event['calendar'] != $ev['calendar'] || $event['recurrence'] ? 2 : 1;
diff --git a/plugins/calendar/calendar_ui.js b/plugins/calendar/calendar_ui.js
index c9334ec6..e7f55cd0 100644
--- a/plugins/calendar/calendar_ui.js
+++ b/plugins/calendar/calendar_ui.js
@@ -2411,6 +2411,7 @@ function rcube_calendar_ui(settings)
         }
 
         // update attendee status
+        attendees = [];
         for (var data, i=0; i < me.selected_event.attendees.length; i++) {
           data = me.selected_event.attendees[i];
           if (settings.identity.emails.indexOf(';'+String(data.email).toLowerCase()) >= 0) {
@@ -2419,6 +2420,7 @@ function rcube_calendar_ui(settings)
 
             if (data.status == 'DELEGATED') {
               data['delegated-to'] = delegate.to;
+              data.rsvp = delegate.rsvp
             }
             else {
               if (data['delegated-to']) {
@@ -2427,6 +2429,8 @@ function rcube_calendar_ui(settings)
                   data.role = 'REQ-PARTICIPANT';
               }
             }
+
+            attendees.push(i)
           }
 
           // set free_busy status to transparent if declined (#4425)
@@ -2459,11 +2463,11 @@ function rcube_calendar_ui(settings)
           });
         }
         else if (settings.invitation_calendars) {
-          update_event('rsvp', submit_data, { status:response, noreply:noreply });
+          update_event('rsvp', submit_data, { status:response, noreply:noreply, attendees:attendees });
         }
         else {
           me.saving_lock = rcmail.set_busy(true, 'calendar.savingdata');
-          rcmail.http_post('event', { action:'rsvp', e:submit_data, status:response, noreply:noreply });
+          rcmail.http_post('event', { action:'rsvp', e:submit_data, status:response, attendees:attendees, noreply:noreply });
         }
 
         event_show_dialog(me.selected_event);
diff --git a/plugins/calendar/drivers/calendar_driver.php b/plugins/calendar/drivers/calendar_driver.php
index aecd2e17..659f4a0e 100644
--- a/plugins/calendar/drivers/calendar_driver.php
+++ b/plugins/calendar/drivers/calendar_driver.php
@@ -197,9 +197,10 @@ abstract class calendar_driver
    *
    * @param array  Hash array with event properties
    * @param string New participant status
+   * @param array  List of hash arrays with updated attendees
    * @return boolean True on success, False on error
    */
-  public function edit_rsvp(&$event, $status)
+  public function edit_rsvp(&$event, $status, $attendees)
   {
     return $this->edit_event($event);
   }
diff --git a/plugins/calendar/drivers/kolab/kolab_driver.php b/plugins/calendar/drivers/kolab/kolab_driver.php
index 5e6f3b38..48dbafd0 100644
--- a/plugins/calendar/drivers/kolab/kolab_driver.php
+++ b/plugins/calendar/drivers/kolab/kolab_driver.php
@@ -619,9 +619,9 @@ class kolab_driver extends calendar_driver
    * @param string New participant status
    * @return boolean True on success, False on error
    */
-  public function edit_rsvp(&$event, $status)
+  public function edit_rsvp(&$event, $status, $attendees)
   {
-    if (($ret = $this->update_event($event)) && $this->rc->config->get('kolab_invitation_calendars')) {
+    if (($ret = $this->update_attendees($event, $attendees)) && $this->rc->config->get('kolab_invitation_calendars')) {
       // re-assign to the according (virtual) calendar
       if (strtoupper($status) == 'DECLINED')
         $event['calendar'] = self::INVITATIONS_CALENDAR_DECLINED;
diff --git a/plugins/libcalendaring/lib/libcalendaring_itip.php b/plugins/libcalendaring/lib/libcalendaring_itip.php
index e7de5c89..41148c60 100644
--- a/plugins/libcalendaring/lib/libcalendaring_itip.php
+++ b/plugins/libcalendaring/lib/libcalendaring_itip.php
@@ -297,9 +297,10 @@ class libcalendaring_itip
      * @param array Event object to delegate
      * @param mixed Delegatee as string or hash array with keys 'name' and 'mailto'
      * @param boolean The delegator's RSVP flag
+     * @param array List with indexes of new/updated attendees
      * @return boolean True on success, False on failure
      */
-    public function delegate_to(&$event, $delegate, $rsvp = false)
+    public function delegate_to(&$event, $delegate, $rsvp = false, &$attendees = array())
     {
         if (is_string($delegate)) {
             $delegates = rcube_mime::decode_address_list($delegate, 1, false);
@@ -345,6 +346,8 @@ class libcalendaring_itip
         $delegate_attendee['delegated-from'] = $me['email'];
         $event['attendees'][$delegate_index] = $delegate_attendee;
 
+        $attendees[] = $delegate_index;
+
         $this->set_sender_email($me['email']);
         return $this->send_itip_message($event, 'REQUEST', $delegate_attendee, 'itipsubjectdelegatedto', 'itipmailbodydelegatedto');
     }