Failover configuration file errors?

[Jason Gerfen]

I am reading the docs regarding failover configuration options and I do 
believe that the syntax I am using is correct but am receiving errors:

dhcpd.conf line 44: invalid statement in peer declaration
         max-unpacked-updates
         ^
Configuration file errors encountered -- exiting

My failover directive is like the following:
#### Failover configuration ####
failover peer "tyr.scl.utah.edu" {
      primary;
      address 155.97.15.2;
      port 519;
      peer address 155.97.15.1;
      peer port 520;
      max-response-delay 30;
      max-unpacked-updates 5;
      mclt 5;
      split 2;
      load balance max seconds 30;
}

Am I missing something? My version information if I overlooked a patch.
Internet Systems Consortium DHCP Server V3.1.1-Gentoo

Thanks in advance.

-- 
Jas