MySQL Forums :: Constraints :: Dual-row primary key and unique constraint

I'm creating a table for language preference. The user settings will include an ordered list of languages.

For this I create a table with 3 INT columns:
user_id
language_id
rank

and define (user_id, language_id) as primary key (a user can't prefer the same language twice), and (user_id, rank) as a unique constraint.

phpAdmin gives me a warning that reads

"PRIMARY and INDEX keys should not both be set for column user_ID"
(I translated the warning from Danish, the wording could be different)

Why is that? Can I ignore this warning?

I'm using phpMyAdmin 2.8.2.4/MySQL clientversion: 5.0.51a