diff --git a/controllers/admin/AdminDeliverySlipController.php b/controllers/admin/AdminDeliverySlipController.php
index 13cdf66de..12f78e455 100644
--- a/controllers/admin/AdminDeliverySlipController.php
+++ b/controllers/admin/AdminDeliverySlipController.php
@@ -47,6 +47,7 @@ class AdminDeliverySlipControllerCore extends AdminController
 						'title' => $this->l('Delivery number:'),
 						'desc' => $this->l('The next delivery slip will begin with this number, and then increase with each additional slip'),
 						'size' => 6,
+						'cast' => 'intval',
 						'type' => 'text'
 					)
 				),