diff --git a/htdocs/core/class/commonobject.class.php b/htdocs/core/class/commonobject.class.php
index 0f53f41e7894b..24ac8762b996a 100644
--- a/htdocs/core/class/commonobject.class.php
+++ b/htdocs/core/class/commonobject.class.php
@@ -1263,7 +1263,7 @@ public function liste_contact($status = -1, $source = 'external', $list = 0, $co
 		if ($source == 'external' || $source == 'thirdparty') {
 			$sql .= " LEFT JOIN ".MAIN_DB_PREFIX."socpeople t on ec.fk_socpeople = t.rowid";
 		}
-		$sql .= " WHERE ec.element_id =".$this->id;
+		$sql .= " WHERE ec.element_id =".((int) $this->id);
 		$sql .= " AND ec.fk_c_type_contact=tc.rowid";
 		$sql .= " AND tc.element='".$this->db->escape($this->element)."'";
 		if ($code) {