Trying to create a GiST index in 7.3

Hi, everybody!

I am trying to create a custom GiST index in 7.3, but getting an error,
that I don't know how to interpret:

testdb=# create table gist_test (field int8);
CREATE TABLE
testdb=#  create index gist_idx on gist_test using gist (field);
ERROR:  data type bigint has no default operator class for access method
"gist"
        You must specify an operator class for the index or define a
        default operator class for the data type
testdb=#

I have done all the setup that was required in 7.2.4:

testdb=#  select * from pg_opclass where opcname = 'gist_index_ops';
-[ RECORD 1 ]+--------------
opcamid      | 783
opcname      | gist_index_ops
opcnamespace |
opcowner     |
opcintype    | 20
opcdefault   | t
opckeytype   | 0


testb=# select * from pg_am where oid=783;
-[ RECORD 1 ]---+-----------------
amname          | gist
amowner         | 1
amstrategies    | 100
amsupport       | 7
amorderstrategy | 0
amcanunique     | f
amcanmulticol   | t
amindexnulls    | f
amconcurrent    | f
amgettuple      | gistgettuple
aminsert        | gistinsert
ambeginscan     | gistbeginscan
amrescan        | gistrescan
amendscan       | gistendscan
ammarkpos       | gistmarkpos
amrestrpos      | gistrestrpos
ambuild         | gistbuild
ambulkdelete    | gistbulkdelete
amcostestimate  | gistcostestimate

rapidb=# select * from pg_type where oid=20;
-[ RECORD 1 ]-+--------
typname       | int8
typnamespace  | 11
typowner      | 1
typlen        | 8
typbyval      | f
typtype       | b
typisdefined  | t
typdelim      | ,
typrelid      | 0
typelem       | 0
typinput      | int8in
typoutput     | int8out
typalign      | d
typstorage    | p
typnotnull    | f
typbasetype   | 0
typtypmod     | -1
typndims      | 0
typdefaultbin |
typdefault    |


Any ideas what's missing? Is there anything new in 7.3, that I have to do?

Thanks a lot!

Dima