diff --git a/hgext/win32mbcs.py b/hgext/win32mbcs.py
--- a/hgext/win32mbcs.py
+++ b/hgext/win32mbcs.py
@@ -156,7 +156,7 @@ funcs = '''os.path.join os.path.split os
 # because they expects argument is local encoded string and cause
 # problem with unicode string.
 rfuncs = '''mercurial.encoding.upper mercurial.encoding.lower
- mercurial.pycompat.bytestr'''
+ mercurial.util._filenamebytestr'''
 
 # List of Windows specific functions to be wrapped.
 winfuncs = '''os.path.splitunc'''
diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -65,6 +65,9 @@ urlerr = pycompat.urlerr
 urlreq = pycompat.urlreq
 xmlrpclib = pycompat.xmlrpclib
 
+# workaround for win32mbcs
+_filenamebytestr = pycompat.bytestr
+
 def isatty(fp):
     try:
         return fp.isatty()
@@ -1224,7 +1227,7 @@ def checkwinfilename(path):
     for n in path.replace('\\', '/').split('/'):
         if not n:
             continue
-        for c in pycompat.bytestr(n):
+        for c in _filenamebytestr(n):
             if c in _winreservedchars:
                 return _("filename contains '%s', which is reserved "
                          "on Windows") % c