diff --git a/addons/sale_order_dates/models/sale_order.py b/addons/sale_order_dates/models/sale_order.py
index 75176271e48..e2ea8b893bb 100644
--- a/addons/sale_order_dates/models/sale_order.py
+++ b/addons/sale_order_dates/models/sale_order.py
@@ -46,7 +46,7 @@ class SaleOrder(models.Model):
             for pick in order.picking_ids:
                 dates_list.append(fields.Datetime.from_string(pick.date))
             if dates_list:
-                order.write({'effective_date': fields.Datetime.to_string(min(dates_list))})
+                order.effective_date = fields.Datetime.to_string(min(dates_list))
 
     @api.onchange('requested_date')
     def onchange_requested_date(self):