diff --git a/interface/lib/classes/tools_sites.inc.php b/interface/lib/classes/tools_sites.inc.php
index b2881f57cc7e28a96554b8f585d17873100035fe..25b7b4b817042188cabca27f74477af62d67d289 100644
--- a/interface/lib/classes/tools_sites.inc.php
+++ b/interface/lib/classes/tools_sites.inc.php
@@ -166,6 +166,9 @@ class tools_sites {
 			$sql .= " sys_groupid IN (".$groups.")";
 		}
 		$sql .= " ORDER BY domain";
+		if ($selected_domain == null) {
+			$selected_domain = '';
+		}
 		return $app->db->queryAllRecords($sql, $not_used_in_table, $selected_domain);
 	}