Show secondary menu in the forum

Hello!

I've encountered a problem. On the website I'm building the menu hierarchy is: members -> sublink under members. I have a menu and a secondary menu, both are displayed when you're at the sublink page. I have placed the default Drupal "forum" under members in the menu, but the forum isn't actually "placed" there, and thus no secondary links show up.

Could I please get some help with this? :)