dynlist: unable to fetch objectClass "groupOfURLs"

Playing on my test server with dynlist, trying to set it up via
cn=config.

I issue -
awilliam@linux-m3mt:~> ldapadd -x -h 172.16.55.129 -D 'cn=Adam
Williams,ou=People,ou=Entities,ou=SAM,o=Morrison Industries,c=US' -W -f
dynlist.ldif 
Enter LDAP Password: 

where dynlist.ldif is -

dn: olcOverlay=dynlist,olcDatabase={1}hdb,cn=config
objectClass: olcOverlayConfig
objectClass: olcDynamicList
olcOverlay: dynlist

- and it fails with error -

adding new entry "olcOverlay=dynlist,olcDatabase={1}hdb,cn=config"
ldap_add: Other (e.g., implementation specific) error (80)
	additional info: unable to fetch objectClass "groupOfURLs"

- and slapd crashes at the next operation.

Anyone recognize that one or know how to work around?  Am I somehow
missing the "groupOfURLs" schema?   If I dump my  cn=SubSchema I don't
see a reference to "groupOfURLs".

Version: Telkomsa openldap2.4-2.4.20-1.el5