diff --git a/mercurial/hgweb/common.py b/mercurial/hgweb/common.py
--- a/mercurial/hgweb/common.py
+++ b/mercurial/hgweb/common.py
@@ -143,7 +143,7 @@ def staticfile(directory, fname, req):
     for part in parts:
         if (part in ('', os.curdir, os.pardir) or
             pycompat.ossep in part or
-            os.altsep is not None and os.altsep in part):
+            pycompat.osaltsep is not None and pycompat.osaltsep in part):
             return
     fpath = os.path.join(*parts)
     if isinstance(directory, str):
diff --git a/mercurial/templater.py b/mercurial/templater.py
--- a/mercurial/templater.py
+++ b/mercurial/templater.py
@@ -1245,7 +1245,7 @@ def stylemap(styles, paths=None):
         if (not style
             or style in (os.curdir, os.pardir)
             or pycompat.ossep in style
-            or os.altsep and os.altsep in style):
+            or pycompat.osaltsep and pycompat.osaltsep in style):
             continue
         locations = [os.path.join(style, 'map'), 'map-' + style]
         locations.append('map')
diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -1304,8 +1304,8 @@ def fspath(name, root):
         return dict((normcase(n), n) for n in os.listdir(dir))
 
     seps = pycompat.ossep
-    if os.altsep:
-        seps = seps + os.altsep
+    if pycompat.osaltsep:
+        seps = seps + pycompat.osaltsep
     # Protect backslashes. This gets silly very quickly.
     seps.replace('\\','\\\\')
     pattern = remod.compile(r'([^%s]+)|([%s]+)' % (seps, seps))
@@ -1371,7 +1371,7 @@ def checknlink(testfile):
 def endswithsep(path):
     '''Check path ends with os.sep or os.altsep.'''
     return (path.endswith(pycompat.ossep)
-            or os.altsep and path.endswith(os.altsep))
+            or pycompat.osaltsep and path.endswith(pycompat.osaltsep))
 
 def splitpath(path):
     '''Split path by os.sep.