diff -r b110dd3d6cea Doc/library/socket.rst
--- a/Doc/library/socket.rst	Thu Jun 02 10:20:16 2016 -0700
+++ b/Doc/library/socket.rst	Thu Jun 02 10:48:08 2016 -0700
@@ -931,12 +931,13 @@
 
 .. method:: socket.fileno()
 
-   Return the socket's file descriptor (a small integer).  This is useful with
-   :func:`select.select`.
+   Return the socket's file descriptor (a small integer), or -1 on failure. This
+   is useful with :func:`select.select`.
 
    Under Windows the small integer returned by this method cannot be used where a
    file descriptor can be used (such as :func:`os.fdopen`).  Unix does not have
-   this limitation.
+   this limitation. In case of failure this method returns -1, it does not raise
+   any exception.
 
 
 .. method:: socket.get_inheritable()