FC5 iptables-restore failure

I've recently been noticing nasty messages come out of FC5:

sony:/home/akpm# service iptables stop
Flushing firewall rules:                                   [  OK  ]
Setting chains to policy ACCEPT: filter                    [  OK  ]
Unloading iptables modules:                                [  OK  ]
sony:/home/akpm# service iptables start
Applying iptables firewall rules: iptables-restore: line 20 failed
                                                           [FAILED]

Dunno when it started happening, but it's in mainline now.

It's a pretty stupid error message.  line 20 of what?

sony:/home/akpm# rpm -q iptables
iptables-1.3.5-1.2