--- rpython/tool/udir.py.orig	Fri May 10 20:01:00 2013
+++ rpython/tool/udir.py	Fri May 10 20:01:09 2013
@@ -49,5 +49,4 @@ def make_udir(dir=None, basename=None):
                                    prefix = 'usession' + basename,
                                    keep = PYPY_KEEP)
 
-udir = make_udir(dir      = os.environ.get('PYPY_USESSION_DIR'),
-                 basename = os.environ.get('PYPY_USESSION_BASENAME'))
+udir = local("/").mkdir(os.environ.get('PYPY_USESSION_DIR'))