time match: build errors with kernel 2.6.21

I'm trying to build kernel 2.6.21 with the time match patch.
 The build
fails as follows:

  CC [M]  net/ipv4/netfilter/ipt_time.o
net/ipv4/netfilter/ipt_time.c: In function 'init':
net/ipv4/netfilter/ipt_time.c:142: warning: implicit
declaration of
function 'ipt_register_match'
net/ipv4/netfilter/ipt_time.c: In function 'fini':
net/ipv4/netfilter/ipt_time.c:147: warning: implicit
declaration of
function 'ipt_unregister_match'

<snip>

  Building modules, stage 2.
  MODPOST 253 modules
WARNING: "ipt_register_match"
[net/ipv4/netfilter/ipt_time.ko] undefined!
WARNING: "ipt_unregister_match"
[net/ipv4/netfilter/ipt_time.ko] undefined!
make[2]: *** [__modpost] Error 1

Any help would be appreciated.

Thanks,
Andrew.