diff --git a/addons/sale/sale.py b/addons/sale/sale.py
index 60ca99bf764..328f0684c24 100644
--- a/addons/sale/sale.py
+++ b/addons/sale/sale.py
@@ -117,7 +117,7 @@ class SaleOrder(models.Model):
         ('cancel', 'Cancelled'),
         ], string='Status', readonly=True, copy=False, index=True, track_visibility='onchange', default='draft')
     date_order = fields.Datetime(string='Order Date', required=True, readonly=True, index=True, states={'draft': [('readonly', False)], 'sent': [('readonly', False)]}, copy=False, default=fields.Datetime.now)
-    validity_date = fields.Date(string='Expiration Date', readonly=True, states={'draft': [('readonly', False)], 'sent': [('readonly', False)]},
+    validity_date = fields.Date(string='Expiration Date', readonly=True, copy=False, states={'draft': [('readonly', False)], 'sent': [('readonly', False)]},
         help="Manually set the expiration date of your quotation (offer), or it will set the date automatically based on the template if online quotation is installed.")
     create_date = fields.Datetime(string='Creation Date', readonly=True, index=True, help="Date on which sales order is created.")
     confirmation_date = fields.Datetime(string='Confirmation Date', readonly=True, index=True, help="Date on which the sale order is confirmed.", oldname="date_confirm")