diff --git a/openerp/addons/base/ir/workflow/workflow.py b/openerp/addons/base/ir/workflow/workflow.py
index cfef52a7b88..dc1fc9afb79 100644
--- a/openerp/addons/base/ir/workflow/workflow.py
+++ b/openerp/addons/base/ir/workflow/workflow.py
@@ -157,7 +157,7 @@ class wkf_workitem(osv.osv):
     _columns = {
         'act_id': fields.many2one('workflow.activity', 'Activity', required=True, ondelete="cascade", select=True),
         'wkf_id': fields.related('act_id','wkf_id', type='many2one', relation='workflow', string='Workflow'),
-        'subflow_id': fields.many2one('workflow.instance', 'Subflow', ondelete="cascade", select=True),
+        'subflow_id': fields.many2one('workflow.instance', 'Subflow', ondelete="set null", select=True),
         'inst_id': fields.many2one('workflow.instance', 'Instance', required=True, ondelete="cascade", select=True),
         'state': fields.char('Status', size=64, select=True),
     }