diff --git a/mercurial/pycompat.py b/mercurial/pycompat.py
--- a/mercurial/pycompat.py
+++ b/mercurial/pycompat.py
@@ -19,6 +19,10 @@
 ispypy = (r'__pypy__' in sys.builtin_module_names)
 isjython = sys.platform.startswith(r'java')
 
+isdarwin = sys.platform == r'darwin'
+isposix = os.name == r'posix'
+iswindows = os.name == r'nt'
+
 if not ispy3:
     import cookielib
     import cPickle as pickle