diff --git a/Lib/os.py b/Lib/os.py
index 4212232..af0ce89 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -6,6 +6,7 @@
 # - os.name is either 'posix' or 'mac'
 # - os.curdir is a string representing the current directory ('.' or ':')
 # - os.pardir is a string representing the parent directory ('..' or '::')
+# - os.sep is the (or a most common) pathname separator ('/' or ':')
 
 # Programs that import and use 'os' stand a better chance of being
 # portable between different platforms.  Of course, they must then
@@ -20,6 +21,7 @@
 	name = 'posix'
 	curdir = '.'
 	pardir = '..'
+	sep = '/'
 	import posixpath
 	path = posixpath
 	del posixpath
@@ -28,6 +30,7 @@
 	name = 'mac'
 	curdir = ':'
 	pardir = '::'
+	sep = ':'
 	import macpath
 	path = macpath
 	del macpath