diff --git a/contrib/wix/dist.wxs b/contrib/wix/dist.wxs
--- a/contrib/wix/dist.wxs
+++ b/contrib/wix/dist.wxs
@@ -15,7 +15,7 @@
         <File Name="mercurial.osutil.pyd" />
         <File Name="mercurial.parsers.pyd" />
         <File Name="pyexpat.pyd" />
-        <File Name="python26.dll" />
+        <File Name="python27.dll" />
         <File Name="bz2.pyd" />
         <File Name="select.pyd" />
         <File Name="unicodedata.pyd" />
diff --git a/hgext/convert/common.py b/hgext/convert/common.py
--- a/hgext/convert/common.py
+++ b/hgext/convert/common.py
@@ -276,9 +276,9 @@ class commandline(object):
                 pass
         cmdline = [util.shellquote(arg) for arg in cmdline]
         if not self.ui.debugflag:
-            cmdline += ['2>', util.nulldev]
+            cmdline += ['2>', os.devnull]
         if closestdin:
-            cmdline += ['<', util.nulldev]
+            cmdline += ['<', os.devnull]
         cmdline = ' '.join(cmdline)
         return cmdline
 
diff --git a/hgext/convert/gnuarch.py b/hgext/convert/gnuarch.py
--- a/hgext/convert/gnuarch.py
+++ b/hgext/convert/gnuarch.py
@@ -184,7 +184,7 @@ class gnuarch_source(converter_source, c
         cmdline = [self.execmd, cmd]
         cmdline += args
         cmdline = [util.shellquote(arg) for arg in cmdline]
-        cmdline += ['>', util.nulldev, '2>', util.nulldev]
+        cmdline += ['>', os.devnull, '2>', os.devnull]
         cmdline = util.quotecommand(' '.join(cmdline))
         self.ui.debug(cmdline, '\n')
         return os.system(cmdline)
diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -515,7 +515,7 @@ def service(opts, parentfn=None, initfn=
         sys.stdout.flush()
         sys.stderr.flush()
 
-        nullfd = os.open(util.nulldev, os.O_RDWR)
+        nullfd = os.open(os.devnull, os.O_RDWR)
         logfilefd = nullfd
         if logfile:
             logfilefd = os.open(logfile, os.O_RDWR | os.O_CREAT | os.O_APPEND)
diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -1998,6 +1998,10 @@ def debuginstall(ui):
         ui.write(_(" (check that your locale is properly set)\n"))
         problems += 1
 
+    # Python lib
+    ui.status(_("checking Python lib (%s)...\n")
+              % os.path.dirname(os.__file__))
+
     # compiled modules
     ui.status(_("checking installed modules (%s)...\n")
               % os.path.dirname(__file__))
diff --git a/mercurial/posix.py b/mercurial/posix.py
--- a/mercurial/posix.py
+++ b/mercurial/posix.py
@@ -10,7 +10,6 @@ import encoding
 import os, sys, errno, stat, getpass, pwd, grp, tempfile, unicodedata
 
 posixfile = open
-nulldev = '/dev/null'
 normpath = os.path.normpath
 samestat = os.path.samestat
 oslink = os.link
diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -45,7 +45,6 @@ makedir = platform.makedir
 nlinks = platform.nlinks
 normpath = platform.normpath
 normcase = platform.normcase
-nulldev = platform.nulldev
 openhardlinks = platform.openhardlinks
 oslink = platform.oslink
 parsepatchoutput = platform.parsepatchoutput
diff --git a/mercurial/windows.py b/mercurial/windows.py
--- a/mercurial/windows.py
+++ b/mercurial/windows.py
@@ -24,7 +24,6 @@ termwidth = win32.termwidth
 testpid = win32.testpid
 unlink = win32.unlink
 
-nulldev = 'NUL:'
 umask = 0022
 
 # wrap osutil.posixfile to provide friendlier exceptions
@@ -174,7 +173,7 @@ def popen(command, mode='r'):
     # Work around "popen spawned process may not write to stdout
     # under windows"
     # http://bugs.python.org/issue1366
-    command += " 2> %s" % nulldev
+    command += " 2> %s" % os.devnull
     return os.popen(quotecommand(command), mode)
 
 def explainexit(code):
diff --git a/tests/test-install.t b/tests/test-install.t
--- a/tests/test-install.t
+++ b/tests/test-install.t
@@ -1,6 +1,7 @@
 hg debuginstall
   $ hg debuginstall
   checking encoding (ascii)...
+  checking Python lib (*lib*)... (glob)
   checking installed modules (*mercurial)... (glob)
   checking templates (*mercurial?templates)... (glob)
   checking commit editor...
@@ -10,6 +11,7 @@ hg debuginstall
 hg debuginstall with no username
   $ HGUSER= hg debuginstall
   checking encoding (ascii)...
+  checking Python lib (*lib*)... (glob)
   checking installed modules (*mercurial)... (glob)
   checking templates (*mercurial?templates)... (glob)
   checking commit editor...