diff --git a/addons/account/invoice.py b/addons/account/invoice.py
index ad38ff87e68..be9b4f63246 100644
--- a/addons/account/invoice.py
+++ b/addons/account/invoice.py
@@ -429,8 +429,9 @@ class account_invoice(osv.osv):
         ait_obj = self.pool.get('account.invoice.tax')
         for id in ids:
             cr.execute("DELETE FROM account_invoice_tax WHERE invoice_id=%s", (id,))
-            partner = self.browse(cr, uid, id).partner_id
-            context.update({'lang': partner.lang})
+            partner = self.browse(cr, uid, id,context=context).partner_id
+            if partner.lang:
+                context.update({'lang': partner.lang})
             for taxe in ait_obj.compute(cr, uid, id, context=context).values():
                 ait_obj.create(cr, uid, taxe)
          # Update the stored value (fields.function), so we write to trigger recompute