diff --git a/bin/addons/base/ir/ir_model.py b/bin/addons/base/ir/ir_model.py
index 5f9e3347b74..19ef96c1e17 100644
--- a/bin/addons/base/ir/ir_model.py
+++ b/bin/addons/base/ir/ir_model.py
@@ -75,10 +75,12 @@ class ir_model(osv.osv):
             fnct_search=_search_osv_memory,
             help="Indicates whether this object model lives in memory only, i.e. is not persisted (osv.osv_memory)")
     }
+    
     _defaults = {
         'model': lambda *a: 'x_',
-        'state': lambda self,cr,uid,ctx={}: (ctx and ctx.get('manual',False)) and 'manual' or 'base',
+        'state': lambda self,cr,uid,ctx=None: (ctx and ctx.get('manual',False)) and 'manual' or 'base',
     }
+    
     def _check_model_name(self, cr, uid, ids):
         for model in self.browse(cr, uid, ids):
             if model.state=='manual':