diff --git a/addons/purchase/purchase.py b/addons/purchase/purchase.py
index 40bfa9cc654..23f889b136f 100644
--- a/addons/purchase/purchase.py
+++ b/addons/purchase/purchase.py
@@ -1208,14 +1208,16 @@ class account_invoice(osv.Model):
         res = super(account_invoice, self).invoice_validate(cr, uid, ids, context=context)
         purchase_order_obj = self.pool.get('purchase.order')
         po_ids = purchase_order_obj.search(cr, uid, [('invoice_ids', 'in', ids)], context=context)
-        purchase_order_obj.message_post(cr, uid, po_ids, body=_("Invoice received"), context=context)
+        if po_ids:
+            purchase_order_obj.message_post(cr, uid, po_ids, body=_("Invoice received"), context=context)
         return res
 
     def confirm_paid(self, cr, uid, ids, context=None):
         res = super(account_invoice, self).confirm_paid(cr, uid, ids, context=context)
         purchase_order_obj = self.pool.get('purchase.order')
         po_ids = purchase_order_obj.search(cr, uid, [('invoice_ids', 'in', ids)], context=context)
-        purchase_order_obj.message_post(cr, uid, po_ids, body=_("Invoice paid"), context=context)
+        if po_ids:
+            purchase_order_obj.message_post(cr, uid, po_ids, body=_("Invoice paid"), context=context)
         return res