Is there a parameter to tell postgresql to not attempt to open an IPv6 socket?

Startup of 8.3.3 on AIX is outputting these messages into the logfile...

        LOG:  could not bind IPv6 socket: The socket name is already in use.
        HINT:  Is another postmaster already running on port 5432? If not, wait a few seconds and retry.

PostgreSQL appears to all intents to startup fine on the UNIX and IPv4
sockets.  Is there a parameter to tell postgresql to not attempt to open
an IPv6 socket?

Thanks,
reid