SSL Server Socket Support in Python?

[=?ISO-8859-1?Q?Andr=E9_S=F8reng?=]

I'm trying to create a SSL-enabled server in Python, and in the doc for
the socket module:

ssl(sock[, keyfile, certfile])
Initiate a SSL connection over the socket sock. keyfile is the
name of a PEM formatted
file that contains your private key. certfile is a PEM formatted
certificate chain file.
On success, a new SSLObject is returned.

So:

listen_socket = socket.socket()
listen_socket.bind((addr, port))
listen_socket.listen(10)
s, addr = listen_socket.accept()
ssl_s = socket.ssl(s, "key.pem", "cert.pem")

socket.sslerror: (1, 'error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol')

Am I missing something?