SQL & PL/SQL

Hello.
I have a question about STRAGG (or wm_concat or any similar) function. I need that STRAGG function returns only distinct values in a row.
My idea was:

select
col1,
stragg(distinct col2)
from
my_table
group by
col1

this select works perfect, but if a have this select in a package, complilation of this package returns ERORR!! PL/SQL: ORA-30482: DISTINCT option not allowed for this function.
What can I do? Is there any other way to get unigue data in stragg output?


Thanks.