MySQL Update Inner Join tables query

I have no idea what the problem is. Using MySQL 5.0 I get a compile error when attempting to run the following MySQL update query: UPDATE b SET b.mapx = g.latitude, b.mapy = g.longitude FROM business AS b INNER JOIN business_geocode g ON b.business_id = g.business_id WHERE (b.mapx = '' OR b.mapx = 0) AND g.latitude > 0 All the field names are correct. Any thoughts?