diff --git a/openerp/tools/config.py b/openerp/tools/config.py
index 8300d6eabf3..c6399db3207 100644
--- a/openerp/tools/config.py
+++ b/openerp/tools/config.py
@@ -624,6 +624,8 @@ class configmanager(object):
 
     def __setitem__(self, key, value):
         self.options[key] = value
+        if isinstance(self.options[key], basestring) and self.casts[key].type in optparse.Option.TYPE_CHECKER:
+            self.options[key] = optparse.Option.TYPE_CHECKER[self.casts[key].type](self.casts[key], key, self.options[key])
 
     def __getitem__(self, key):
         return self.options[key]