diff --git a/controllers/admin/AdminInvoicesController.php b/controllers/admin/AdminInvoicesController.php
index c90344b84..57fba9bd0 100644
--- a/controllers/admin/AdminInvoicesController.php
+++ b/controllers/admin/AdminInvoicesController.php
@@ -213,7 +213,7 @@ class AdminInvoicesControllerCore extends AdminController
 
 	public function postProcess()
 	{
-		if (Tools::getValue('submitAddinvoice_date'))
+		if (Tools::isSubmit('submitAddinvoice_date'))
 		{
 			if (!Validate::isDate(Tools::getValue('date_from')))
 				$this->errors[] = $this->l('Invalid "From" date');