/etc/rc: WARNING: domainname(1) is not set.

Hi,
I have been getting the message "/etc/rc: WARNING: domainname(1) is not 
set" every time I boot one of my machines.
It is a 5.1-CURRENT system but I have not updated since June 15.

I have been ignoring this for some time because I have been trying to 
get DDNS to work.
I thought it was related to my DDNS problem.  Now that I have DDNS 
working (finally) I was supprised to see the message still appearing.

I couldn't find anything in the archives.
Suggestions?

I know it is protocol but please CC me on any replies.  I subscribe to 
CURRENT as a digest.  Replying via the digest is a pain.
TIA.