diff --git a/addons/account_discount/models/account_invoice.py b/addons/account_discount/models/account_invoice.py
index e4ae74d1..61be6c4c 100644
--- a/addons/account_discount/models/account_invoice.py
+++ b/addons/account_discount/models/account_invoice.py
@@ -43,7 +43,8 @@ class AccountInvoice(models.Model):
         self._check_constrains()
         for line in self.invoice_line_ids:
             line.write({'discount': 0.0})
-        amount_untaxed = self.amount_untaxed
+        # amount_untaxed = self.amount_untaxed
+        gross_amount = self.gross_amount
         if self.discount_method == 'per':
             for line in self.invoice_line_ids:
                 line.write({'discount': line.discount + self.discount_per})
@@ -51,7 +52,7 @@ class AccountInvoice(models.Model):
             for line in self.invoice_line_ids:
                 discount_value_ratio = \
                     (self.discount_amount * line.price_subtotal) / \
-                    amount_untaxed
+                    gross_amount
                 discount_per_ratio = \
                     (discount_value_ratio * 100) / line.price_subtotal
                 line.write({'discount': line.discount + discount_per_ratio})