Missing parameter aria_pagecache_buffer_size for rds mariadb

I am having some issue with my mariadb instance as described here: https://forums.aws.amazon.com/thread.jspa?messageID=921037#921037
In order to fix it I was trying to increase the aria_pagecache_buffer_size for the database from the standard 128MB. From what I could read online this should be way higher. However this parameter is missing. How can I change it?