PF not loading at boot time

[Doug Niven]

I've got a PF anchor referenced in my /etc/pf.conf file here:

    table <goodguys> { 111.222.0.0/16, 222.222.0.0/16 }
    block in proto tcp from any to any port 22
    pass in on en0 proto tcp from <goodguys> to en0 port 22 flags S/SA keep state

But while the /etc/pf.conf file loads fine manually, it does not load at boot, generating the following error in my log:

    no IP address found for en0
    /etc/pf.anchors/my-anchor:6: could not parse host specification
    pfctl: Syntax error in config file: pf rules not loaded

I suspect this is because at the time PF loads at boot, en0 doesn't yet have an IP address or network state.

Is there any other way I might be able to write this rule to avoid this problem?

Thanks in advance,

Doug