diff --git a/sale.py b/sale.py
index f8b896c3c5..bcf7d3201a 100644
--- a/sale.py
+++ b/sale.py
@@ -67,7 +67,8 @@ class Sale(Workflow, ModelSQL, ModelView):
         depends=['state'])
     party = fields.Many2One('party.party', 'Party', required=True, select=True,
         states={
-            'readonly': Eval('state') != 'draft',
+            'readonly': ((Eval('state') != 'draft')
+                | (Eval('lines', [0]) & Eval('party'))),
             },
         depends=['state'])
     party_lang = fields.Function(fields.Char('Party Language'),