diff --git a/CHANGELOG b/CHANGELOG
index 3ef7da2677..9de3e9ae16 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,5 @@
+* Allow sale without payment term
+
 Version 4.0.0 - 2016-05-02
 * Bug fixes (see mercurial logs for details)
 * Rename Sale reference into number and add reference
diff --git a/sale.py b/sale.py
index a7e6d6e023..1e3a4ce24f 100644
--- a/sale.py
+++ b/sale.py
@@ -66,7 +66,8 @@ class Sale(Workflow, ModelSQL, ModelView, TaxableMixin):
             },
         depends=['state'])
     payment_term = fields.Many2One('account.invoice.payment_term',
-        'Payment Term', required=True, states={
+        'Payment Term',
+        states={
             'readonly': Eval('state') != 'draft',
             },
         depends=['state'])
@@ -341,6 +342,9 @@ class Sale(Workflow, ModelSQL, ModelView, TaxableMixin):
         table = TableHandler(cls, module_name)
         table.index_action('create_date', action='add')
 
+        # Migration from 4.0: Drop not null on payment_term
+        table.not_null_action('payment_term', 'remove')
+
     @classmethod
     def default_payment_term(cls):
         PaymentTerm = Pool().get('account.invoice.payment_term')