diff --git a/plugins/calendar/calendar.php b/plugins/calendar/calendar.php
index 28372491..d50a0682 100644
--- a/plugins/calendar/calendar.php
+++ b/plugins/calendar/calendar.php
@@ -855,6 +855,11 @@ class calendar extends rcube_plugin
    */
   public function attachment_upload()
   {
+    // Upload progress update
+    if (!empty($_GET['_progress'])) {
+      rcube_upload_progress();
+    }
+
     $event    = get_input_value('_id', RCUBE_INPUT_GPC);
     $calendar = get_input_value('calendar', RCUBE_INPUT_GPC);
     $uploadid = get_input_value('_uploadid', RCUBE_INPUT_GPC);
diff --git a/plugins/calendar/lib/calendar_ui.php b/plugins/calendar/lib/calendar_ui.php
index 2c24d62f..5fae6e3f 100644
--- a/plugins/calendar/lib/calendar_ui.php
+++ b/plugins/calendar/lib/calendar_ui.php
@@ -350,7 +350,7 @@ class calendar_ui
       case 'monthly':
         $select = $this->interval_selector(array('name' => 'interval', 'class' => 'edit-recurrence-interval', 'id' => 'edit-recurrence-interval-monthly'));
         $html = html::div($attrib, html::label(null, $this->calendar->gettext('every')) . $select->show(1) . html::span('label-after', $this->calendar->gettext('months')));
-        
+
 /* multiple month selection is not supported by Kolab
         $checkbox = new html_radiobutton(array('name' => 'bymonthday', 'class' => 'edit-recurrence-monthly-bymonthday'));
         for ($monthdays = '', $d = 1; $d <= 31; $d++) {
@@ -471,6 +471,9 @@ class calendar_ui
     if (!$attrib['id'])
       $attrib['id'] = 'rcmUploadForm';
 
+    // Enable upload progress bar
+    rcube_upload_progress_init();
+
     // find max filesize value
     $max_filesize = parse_bytes(ini_get('upload_max_filesize'));
     $max_postsize = parse_bytes(ini_get('post_max_size'));