Local user of a subwiki loses ability to view the public main wiki when they are logged in

I have a main wiki that is public (anyone can view on our LAN) but with only a select group of global users. There are also several sub-wikis each with their own local users representing different teams in our company.

When someone who is not logged in visits the site, they can view the main wiki just fine. However, if they log into one of the sub-wikis, they can no longer view any content on the main wiki.

Is there any way to make the main wiki viewable to users of sub-wikis when they are logged in without making them members of the main wiki? I want to keep the main wiki available for reference while local users are editing their sub-wikis.