diff --git a/sale.py b/sale.py
index 98c2374..1f9905a 100644
--- a/sale.py
+++ b/sale.py
@@ -196,7 +196,7 @@ class WizardSalePayment(Wizard):
         active_id = Transaction().context.get('active_id', False)
         sale = Sale(active_id)
         if not sale.reference:
-            Sale.set_reference([sale])
+            Sale.set_number([sale])
 
         account = (sale.party.account_receivable
             and sale.party.account_receivable.id