PostgreSQL EXCLUDE USING error: Data type integer has no default operator class

Question

In PostgreSQL 9.2.3 I am trying to create this simplified table:

CREATE TABLE test (
    user_id INTEGER,
    startend TSTZRANGE,
    EXCLUDE USING gist (user_id WITH =, startend WITH &&)
);

But I get this error:

ERROR:  data type integer has no default operator class for access method "gist"
HINT:  You must specify an operator class for the index or define
       a default operator class for the data type.

The PostgreSQL docs use this example which does not work for me:

CREATE TABLE room_reservation (
    room text,
    during tsrange,
    EXCLUDE USING gist (room WITH =, during WITH &&)
);

Same error message.

And this one, which does not work for me either:

CREATE TABLE zoo (
    cage   INTEGER,
    animal TEXT,
    EXCLUDE USING gist (cage WITH =, animal WITH <>)
);

Same error message.

I am able to create this without any problem:

CREATE TABLE test (
    user_id INTEGER,
    startend TSTZRANGE,
    EXCLUDE USING gist (startend WITH &&)
);

and this:

CREATE TABLE test (
    user_id INTEGER,
    startend TSTZRANGE,
    EXCLUDE USING btree (user_id WITH =)
);

I've spent quite a bit of time searching for hints about figuring out how to make this work, or figuring out why it won't work. Any ideas?