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