ipfilter 4.1.8 compilation on FreeBSD 5.4

Hello,
I'm trying to get ipfilter 4.1.8 going on FreeBSD 5.4-release. I've got
the tarball, extracted it in the /usr/src area with the sources and ran
make freebsd5
which seemed to go fine. Then i ran
BSD/kupgrade
which tried to install but failed with the error:
cp: mlfk_ipl.c: no such file or directory
I'm trying to set the firewall up as a loadable kernel module, with a
default block policy, and i'd like to hook in altq bandwidth controls. I'm
wondering if i also need ipv6 as i won't be using it for anything?
Thanks.
Dave.