diff --git a/core/apps/orders/serializers/party.py b/core/apps/orders/serializers/party.py
index a31baaf..e6868f1 100644
--- a/core/apps/orders/serializers/party.py
+++ b/core/apps/orders/serializers/party.py
@@ -352,8 +352,12 @@ class PartyUpdateSerializer(serializers.ModelSerializer):
             )
             party_amount = PartyAmount.objects.get(party=instance)
             party_amount.total_price = total_price
-            party_amount.cost_amount = total_price - instance.discount
-            party_amount.payment_amount = total_price - instance.discount
+            party_amount.cost_amount = (
+                total_price - instance.discount if instance.discount else 0
+            )
+            party_amount.payment_amount = (
+                total_price - instance.discount if instance.discount else 0
+            )
             party_amount.save()
             return instance