diff --git a/sale.py b/sale.py
index 7e36409..3c63fab 100644
--- a/sale.py
+++ b/sale.py
@@ -84,7 +84,12 @@ class Sale(metaclass=PoolMeta):
         if self.payment_type and self.payment_type.kind == 'both':
             return self.payment_type
 
-        if invoice.untaxed_amount >= ZERO:
+        if hasattr(invoice, 'untaxed_amount'):
+            untaxed_amount = invoice.untaxed_amount
+        else:
+            untaxed_amount = sum(l.on_change_with_amount() for l in invoice.lines)
+
+        if untaxed_amount >= ZERO:
             kind = 'receivable'
             name = 'customer_payment_type'
         else: