diff --git a/models/sale.py b/models/sale.py
index 529d617cb06b87b4ec0490c4396a056d784b5b72..3c46b77bfb81af086754ebac6e416cd8772bbc8e 100644
--- a/models/sale.py
+++ b/models/sale.py
@@ -19,7 +19,7 @@ class SaleOrder(models.Model):
         for order in self:
             line_to_invoice = [line for line in order.order_line if line.invoice_status == 'to invoice']
 
-            untaxed_amount_to_invoice = self.amount_untaxed 
+            untaxed_amount_to_invoice = order.amount_untaxed 
             for line in line_to_invoice:
                 untaxed_amount_to_invoice -= line.qty_invoiced * line.price_unit