diff --git a/addons/sale/sale.py b/addons/sale/sale.py
index e71199ab30e..09ee8d5e3fd 100644
--- a/addons/sale/sale.py
+++ b/addons/sale/sale.py
@@ -1020,7 +1020,8 @@ class account_invoice(osv.Model):
         sale_order_obj = self.pool.get('sale.order')
         res = super(account_invoice, self).confirm_paid(cr, uid, ids, context=context)
         so_ids = sale_order_obj.search(cr, uid, [('invoice_ids', 'in', ids)], context=context)
-        sale_order_obj.message_post(cr, uid, so_ids, body=_("Invoice paid"), context=context)
+        if so_ids:
+            sale_order_obj.message_post(cr, uid, so_ids, body=_("Invoice paid"), context=context)
         return res
 
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