diff --git a/addons/event_sale/event_sale.py b/addons/event_sale/event_sale.py
index f37dea3f075..2dd40a7c285 100644
--- a/addons/event_sale/event_sale.py
+++ b/addons/event_sale/event_sale.py
@@ -40,7 +40,7 @@ class sale_order_line(osv.osv):
         'event_id': fields.many2one('event.event', 'Event', help="Choose an event and it will automatically create a registration for this event."),
         #those 2 fields are used for dynamic domains and filled by onchange
         'event_type_id': fields.related('event_type_id', type='many2one', relation="event.type", string="Event Type"),
-        'event_ok': fields.related('event_ok', string='event_ok', type='boolean'),
+        'event_ok': fields.related('product_id', 'event_ok', string='event_ok', type='boolean'),
     }
 
     def product_id_change(self, cr, uid, ids,