diff --git a/mercurial/windows.py b/mercurial/windows.py
--- a/mercurial/windows.py
+++ b/mercurial/windows.py
@@ -8,6 +8,7 @@
 from i18n import _
 import osutil, error
 import errno, msvcrt, os, re, sys
+from mercurial import win32
 
 nulldev = 'NUL:'
 umask = 002
@@ -17,7 +18,7 @@ def posixfile(name, mode='r', buffering=
     try:
         return osutil.posixfile(name, mode, buffering)
     except WindowsError, err:
-        raise WinIOError(err)
+        raise win32.WinIOError(err)
 posixfile.__doc__ = osutil.posixfile.__doc__
 
 class winstdout(object):