How to access (local) ghost installation via IP


I installed ghost for testing on a Raspberry Pi. I set up a dDNS domain and forwarded the :80 from my router to the raspi. I can access the installation from outside my local network just fine.
I can’t, however, access it from within my local network, because that the router basically would need to connect to itself. If I enter the raspi’s local IP directly, I can’t connect to the ghost installation, too. Probably nginx isn’t configured to listen to it/reverse proxy it.

How do I do that?