diff --git a/controllers/admin/AdminCustomersController.php b/controllers/admin/AdminCustomersController.php
index 47fddd1d8..3b9d3bba1 100644
--- a/controllers/admin/AdminCustomersController.php
+++ b/controllers/admin/AdminCustomersController.php
@@ -212,7 +212,7 @@ class AdminCustomersControllerCore extends AdminController
 
 	public function renderList()
 	{
-		$this->_select = '(YEAR(CURRENT_DATE)-YEAR(`birthday`)) - (RIGHT(CURRENT_DATE, 5) < RIGHT(birthday, 5)) AS `age`, (
+		$this->_select = 'IF (YEAR(`birthday`) = 0, "-", (YEAR(CURRENT_DATE)-YEAR(`birthday`)) - (RIGHT(CURRENT_DATE, 5) < RIGHT(birthday, 5))) AS `age`, (
 			SELECT c.date_add FROM '._DB_PREFIX_.'guest g
 			LEFT JOIN '._DB_PREFIX_.'connections c ON c.id_guest = g.id_guest
 			WHERE g.id_customer = a.id_customer