diff --git a/modules/monitoring/library/Monitoring/Backend/Ido/Query/HostnotificationQuery.php b/modules/monitoring/library/Monitoring/Backend/Ido/Query/HostnotificationQuery.php
index 284468ed7..f252a7e8e 100644
--- a/modules/monitoring/library/Monitoring/Backend/Ido/Query/HostnotificationQuery.php
+++ b/modules/monitoring/library/Monitoring/Backend/Ido/Query/HostnotificationQuery.php
@@ -104,6 +104,7 @@ class HostnotificationQuery extends IdoQuery
      */
     protected function joinBaseTables()
     {
+        $concattedContacts = null;
         switch ($this->ds->getDbType()) {
             case 'mysql':
                 $concattedContacts = "GROUP_CONCAT("