diff --git a/plugins/libkolab/lib/kolab_format_event.php b/plugins/libkolab/lib/kolab_format_event.php
index e59ddcf8..57c19bee 100644
--- a/plugins/libkolab/lib/kolab_format_event.php
+++ b/plugins/libkolab/lib/kolab_format_event.php
@@ -123,6 +123,7 @@ class kolab_format_event extends kolab_format_xcal
 
                 // write cleaned-up exception data back to memory/cache
                 $object['exceptions'][$i] = $this->expand_exception($exevent->data, $object);
+                $object['exceptions'][$i]['_instance'] = $compacted['_instance'];
             }
             $this->obj->setExceptions($vexceptions);