diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
--- a/mercurial/dirstate.py
+++ b/mercurial/dirstate.py
@@ -286,7 +286,7 @@ class dirstate(object):
         # self._root ends with a path separator if self._root is '/' or 'C:\'
         rootsep = self._root
         if not util.endswithsep(rootsep):
-            rootsep += os.sep
+            rootsep += pycompat.ossep
         if cwd.startswith(rootsep):
             return cwd[len(rootsep):]
         else:
diff --git a/mercurial/pathutil.py b/mercurial/pathutil.py
--- a/mercurial/pathutil.py
+++ b/mercurial/pathutil.py
@@ -9,6 +9,7 @@ from .i18n import _
 from . import (
     encoding,
     error,
+    pycompat,
     util,
 )
 
@@ -87,8 +88,8 @@ class pathauditor(object):
         # This means we won't accidentally traverse a symlink into some other
         # filesystem (which is potentially expensive to access).
         for i in range(len(parts)):
-            prefix = os.sep.join(parts[:i + 1])
-            normprefix = os.sep.join(normparts[:i + 1])
+            prefix = pycompat.ossep.join(parts[:i + 1])
+            normprefix = pycompat.ossep.join(normparts[:i + 1])
             if normprefix in self.auditeddir:
                 continue
             if self._realfs:
@@ -132,7 +133,7 @@ def canonpath(root, cwd, myname, auditor
     if util.endswithsep(root):
         rootsep = root
     else:
-        rootsep = root + os.sep
+        rootsep = root + pycompat.ossep
     name = myname
     if not os.path.isabs(name):
         name = os.path.join(root, cwd, name)
@@ -202,8 +203,8 @@ def normasprefix(path):
     '/'
     '''
     d, p = os.path.splitdrive(path)
-    if len(p) != len(os.sep):
-        return path + os.sep
+    if len(p) != len(pycompat.ossep):
+        return path + pycompat.ossep
     else:
         return path
 
diff --git a/mercurial/posix.py b/mercurial/posix.py
--- a/mercurial/posix.py
+++ b/mercurial/posix.py
@@ -369,7 +369,7 @@ if sys.platform == 'cygwin':
     # use upper-ing as normcase as same as NTFS workaround
     def normcase(path):
         pathlen = len(path)
-        if (pathlen == 0) or (path[0] != os.sep):
+        if (pathlen == 0) or (path[0] != pycompat.ossep):
             # treat as relative
             return encoding.upper(path)
 
@@ -381,7 +381,7 @@ if sys.platform == 'cygwin':
             mplen = len(mp)
             if mplen == pathlen: # mount point itself
                 return mp
-            if path[mplen] == os.sep:
+            if path[mplen] == pycompat.ossep:
                 return mp + encoding.upper(path[mplen:])
 
         return encoding.upper(path)
@@ -456,7 +456,7 @@ def findexe(command):
             return executable
         return None
 
-    if os.sep in command:
+    if pycompat.ossep in command:
         return findexisting(command)
 
     if sys.platform == 'plan9':