diff --git a/contract/models/contract.py b/contract/models/contract.py
index 87156c85..abe72816 100644
--- a/contract/models/contract.py
+++ b/contract/models/contract.py
@@ -297,9 +297,11 @@ class AccountAnalyticAccount(models.Model):
         :return: contract lines (account.analytic.invoice.line recordset)
         """
         self.ensure_one()
-        return self.recurring_invoice_line_ids.filtered(
-            lambda l: not l.is_canceled and l.recurring_next_date
-            and l.recurring_next_date <= date_ref)
+        if date_ref:
+            return self.recurring_invoice_line_ids.filtered(
+                lambda l: not l.is_canceled and l.recurring_next_date
+                and l.recurring_next_date <= date_ref)
+        return False
 
     @api.multi
     def _prepare_recurring_invoices_values(self, date_ref=False):
diff --git a/contract/models/contract_line.py b/contract/models/contract_line.py
index c87abf91..d0addafb 100644
--- a/contract/models/contract_line.py
+++ b/contract/models/contract_line.py
@@ -282,15 +282,6 @@ class AccountAnalyticInvoiceLine(models.Model):
                     % rec.name
                 )
 
-    @api.constrains('date_start')
-    def _check_date_start_recurring_invoices(self):
-        for line in self.filtered('contract_id.recurring_invoices'):
-            if not line.date_start:
-                raise ValidationError(
-                    _("You must supply a start date for contract line '%s'")
-                    % line.name
-                )
-
     @api.constrains('date_start', 'date_end')
     def _check_start_end_dates(self):
         for line in self.filtered('date_end'):
diff --git a/contract/tests/test_contract.py b/contract/tests/test_contract.py
index b1482d03..a15fb0e6 100644
--- a/contract/tests/test_contract.py
+++ b/contract/tests/test_contract.py
@@ -417,11 +417,6 @@ class TestContract(TestContractBase):
             self.contract.write({'recurring_invoices': True})
             self.acct_line.write({'recurring_next_date': False})
 
-    def test_check_date_start_recurring_invoices(self):
-        with self.assertRaises(ValidationError):
-            self.contract.write({'recurring_invoices': True})
-            self.acct_line.write({'date_start': False})
-
     def test_onchange_contract_template_id(self):
         """It should change the contract values to match the template."""
         self.contract.contract_template_id = self.template