diff --git a/payment.py b/payment.py
index 32089fab4f..797567a36d 100644
--- a/payment.py
+++ b/payment.py
@@ -307,6 +307,7 @@ class Mandate(Workflow, ModelSQL, ModelView):
             },
         depends=['state'])
     account_number = fields.Many2One('bank.account.number', 'Account Number',
+        ondelete='RESTRICT',
         states={
             'readonly': Eval('state').in_(['validated', 'canceled']),
             'required': Eval('state') == 'validated',