PostgreSQL Sub-Select Query

I have the following 2 tables:

dbfp_dev=# select * from usrdtls_usrgrps;
usrdtls_usrgrps_id | userid | usergroupid
-------------------------+--- -----+-------------
1 | 1 | 1
2 | 4 | 5
3 | 5 | 5

dbfp_dev=# select userid, username, usertype from userdetails;
userid | username | usertype
---------+--------------+-----------
1 | admin | system
4 | melvin | affiliate
5 | jane | affiliate


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.....and I run this sub-select query statement:

dbfp_dev=# select userid from usrdtls_usrgrps where usergroupid='5' and userid in (select userid from userdetails order by username asc);
userid
--------
4
5


It returns to me the userid in the order 4, 5, meaning melvin, followed by jane. However I want the userids returned to be sorted by asc, meaning, jane, followed by melvin, which is 5 then 4.....NOT 4, then 5. What is wrong? Hope I made myself clear =D...any ideas please?