SELECT DISTINCT ON bug?

The following query give an error in 7.3

TAL=# SELECT distinct on(dai_genres.id), dsc from dai_genres,
rel_genres_goods where dai_genres.id=rel_genres_goods.major_id group by
id, dsc;
ERROR:  parser: parse error at or near "," at character 34

I looked up the 7.3 docs and I thought I had the syntax right.

What's the proper syntaxt for the above query (selecting unique id's and
their associated dsc from the two tables joined on id=major_id)

Thanks.

PS I was doing this query using GROUP BY but using distinct (on) seems
like it should be faster, but I can't test it until I get the query
running ...

--

Jean-Christian Imbeault