OpenBGPd: received notification: error in OPEN message, unsupported capability

I was attempting to setup OpenBGPd to use on my IPv6 only BGP setup, but I kept seeing the following errors while talking to a Quagga BGP peer.

Apr 17 22:59:57 hyrum bgpd[54087]: neighbor 2001:xxxx:xxxx:e::1 (SJC): received notification: error in OPEN message, unsupported capability
Apr 17 22:59:57 hyrum bgpd[54087]: neighbor 2001:xxxx:xxxx:e::1 (SJC): disabling multiprotocol capability
Apr 17 22:59:57 hyrum bgpd[54087]: neighbor 2001:xxxx:xxxx:e::1 (SJC): session_setup_socket set sockopt hoplimit: Protocol not available
Apr 17 23:00:04 hyrum bgpd[54087]: neighbor 2001:xxxx:xxxx:e::1 (SJC): session_setup_socket set sockopt hoplimit: Protocol not available

I discovered a mailing list post from Henning Brauer, an author of OpenBGPd, talking about how to fix the problem. It took a few tries to figure out exactly how to accomplish what he suggested.

I tried the following:

neighbor $sjc {
        remote-as 1
        announce IPv4 none
        descr SJC
}

That didn't work, but this does:

neighbor $sjc {
        remote-as 1
        announce IPv6 unicast
        descr SJC
}