Index: Doc/library/os.path.rst
===================================================================
--- Doc/library/os.path.rst	(revision 77150)
+++ Doc/library/os.path.rst	(working copy)
@@ -218,12 +218,12 @@
    links encountered in the path (if they are supported by the operating system).
 
 
-.. function:: relpath(path, start=None)
+.. function:: relpath(path, start=os.curdir)
 
    Return a relative filepath to *path* either from the current directory or from
    an optional *start* point.
 
-   *start* defaults to :attr:`os.curdir`. Availability:  Windows, Unix.
+   Availability:  Windows, Unix.
 
 
 .. function:: samefile(path1, path2)
Index: Lib/posixpath.py
===================================================================
--- Lib/posixpath.py	(revision 77150)
+++ Lib/posixpath.py	(working copy)
@@ -423,7 +423,7 @@
 
 supports_unicode_filenames = False
 
-def relpath(path, start=None):
+def relpath(path, start=curdir):
     """Return a relative version of a path"""
 
     if not path:
@@ -433,14 +433,14 @@
         curdir = b'.'
         sep = b'/'
         pardir = b'..'
+        # If start is the str of curdir (default), set it to bytes
+        if start == curdir.decode(sys.getfilesystemencoding()):
+            start = curdir
     else:
         curdir = '.'
         sep = '/'
         pardir = '..'
 
-    if start is None:
-        start = curdir
-
     start_list = abspath(start).split(sep)
     path_list = abspath(path).split(sep)