diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index aa95d1dac04..f3485cca57c 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -588,7 +588,7 @@ The following constants are options for the *flags* parameter to the
 :func:`~os.open` function.  They can be combined using the bitwise OR operator
 ``|``.  Some of them are not available on all platforms.  For descriptions of
 their availability and use, consult the :manpage:`open(2)` manual page on Unix
-or `the MSDN <http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>` on Windows.
+or `the MSDN <http://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windows.
 
 
 .. data:: O_RDONLY