diff --git a/addons/sale/models/sale.py b/addons/sale/models/sale.py
index e8954205d2e..d190f32f70d 100644
--- a/addons/sale/models/sale.py
+++ b/addons/sale/models/sale.py
@@ -1640,7 +1640,7 @@ class SaleOrderLine(models.Model):
                     new_list_price, self.order_id.pricelist_id.currency_id,
                     self.order_id.company_id, self.order_id.date_order or fields.Date.today())
             discount = (new_list_price - price) / new_list_price * 100
-            if discount > 0:
+            if (discount > 0 and new_list_price > 0) or (discount < 0 and new_list_price < 0):
                 self.discount = discount
 
     def _is_delivery(self):