diff --git a/hgext/convert/cvsps.py b/hgext/convert/cvsps.py
--- a/hgext/convert/cvsps.py
+++ b/hgext/convert/cvsps.py
@@ -12,6 +12,7 @@ import re
 from mercurial.i18n import _
 from mercurial import (
     hook,
+    pycompat,
     util,
 )
 
@@ -136,8 +137,8 @@ def createlog(ui, directory=None, root="
         except IOError:
             raise logerror(_('not a CVS sandbox'))
 
-        if prefix and not prefix.endswith(os.sep):
-            prefix += os.sep
+        if prefix and not prefix.endswith(pycompat.ossep):
+            prefix += pycompat.ossep
 
         # Use the Root file in the sandbox, if it exists
         try:
diff --git a/hgext/win32mbcs.py b/hgext/win32mbcs.py
--- a/hgext/win32mbcs.py
+++ b/hgext/win32mbcs.py
@@ -53,6 +53,7 @@ from mercurial.i18n import _
 from mercurial import (
     encoding,
     error,
+    pycompat,
 )
 
 # Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
@@ -97,7 +98,7 @@ def appendsep(s):
     except UnicodeError:
         us = s
     if us and us[-1] not in ':/\\':
-        s += os.sep
+        s += pycompat.ossep
     return s