How can I connect to the same server in multiple irssi instances?

I have an irssi session which is connected to Freenode (via /server fn), in which I am in multiple related channels. This session is inside of a tmux instance which has other terminals, also related to this topic. I have set irssi to automatically authenticate me via NickServ. Now I want to open a completely separate terminal and connect to Freenode via irssi again, so I can join an unrelated channel. However, when I open irssi and /server fn again, it fails to authenticate me as I am already connected to the server in the other irssi session. I can connect to the same server with different authenticated accounts, but I want to have multiple irssi instances authenticated with the same account. Is there any way I can be connected to the same server (but have different channels open) in two separate irssi instances?