diff --git a/CHANGELOG b/CHANGELOG
index 97c6c0bbae..6d313f4073 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,5 @@
+* Make payment term not required
+
 Version 4.0.0 - 2016-05-02
 * Bug fixes (see mercurial logs for details)
 * Merge invoice and credit note
diff --git a/invoice.odt b/invoice.odt
index 28dd18fc43..e2f392b9d3 100644
Binary files a/invoice.odt and b/invoice.odt differ
diff --git a/invoice.py b/invoice.py
index 4a8e5fb0df..2888303d58 100644
--- a/invoice.py
+++ b/invoice.py
@@ -129,7 +129,7 @@ class Invoice(Workflow, ModelSQL, ModelView, TaxableMixin):
                 ('kind', '=', 'payable')),
             ])
     payment_term = fields.Many2One('account.invoice.payment_term',
-        'Payment Term', required=True, states=_STATES, depends=_DEPENDS)
+        'Payment Term', states=_STATES, depends=_DEPENDS)
     lines = fields.One2Many('account.invoice.line', 'invoice', 'Lines',
         domain=[
             ('company', '=', Eval('company', -1)),
@@ -359,6 +359,9 @@ class Invoice(Workflow, ModelSQL, ModelView, TaxableMixin):
         # Add index on create_date
         table.index_action('create_date', action='add')
 
+        # Migration from 4.0: Drop not null on payment_term
+        table.not_null_action('payment_term', 'remove')
+
     @staticmethod
     def default_type():
         return Transaction().context.get('type', 'out')
@@ -937,11 +940,11 @@ class Invoice(Workflow, ModelSQL, ModelView, TaxableMixin):
             if line['amount_second_currency']:
                 total_currency += line['amount_second_currency']
 
-        term_lines = self.payment_term.compute(total, self.company.currency,
-            self.invoice_date)
+        term_lines = [(Date.today(), total)]
+        if self.payment_term:
+            term_lines = self.payment_term.compute(
+                total, self.company.currency, self.invoice_date)
         remainder_total_currency = total_currency
-        if not term_lines:
-            term_lines = [(Date.today(), total)]
         for date, amount in term_lines:
             val = self._get_move_line(date, amount)
             if val['amount_second_currency']: