diff --git a/sale.py b/sale.py
index aa31823..3cc9a74 100644
--- a/sale.py
+++ b/sale.py
@@ -433,7 +433,7 @@ class Sale(metaclass=PoolMeta):
         delivery = args.get('delivery_amount', 0)
         if args.get('delivery_invoice') and delivery and int(delivery) > 0:
             product = config.delivery_product
-            args['lines'].append({
+            lines.append({
                 'product': product.id,
                 'quantity': 1,
                 'type': 'line',