syntax error at or near "gist_trgm_ops" on debian

Hello Postgres users,

I'm Philippe from switzerland,

I want to build a trigram index in a mycology database of mine,
currently running on a debian laptop, and facing the following issue:

diskpix=> CREATE INDEX idx_trgm_genus ON myco.genus USING GIST
(myco.genus.name gist_trgm_ops);
ERROR:  syntax error at or near "gist_trgm_ops"
LINE 1: ...m_genus ON myco.genus USING GIST (myco.genus.name gist_trgm_...

I've installed the postgresql-contrib package, rebooted my box, then
created the trgm extension using:

CREATE EXTENSION pg_trgm;

But it still does not work, what am I missing?

--
Philippe Strauss
https://straussengineering.ch/