BIND zones added manually to config file not appearing in Webmin

I‘m just in the process of rebuilding a system which includes BIND and Webmin. Zone files for BIND are on an external disk, which worked fine on the previous setup. After installing the server from scratch, I went into webmin and edited /etc/bind/named.conf.default-zones, adding the entries for the zone files as they were on the old setup, then restarted BIND. If I query one of these zones (using nslookup and first setting server 127.0.0.1), I can resolve names in these zones. However, Webmin tells me there are no DNS zones defined for this name server. Restarting BIND through Webmin, reloading Webmin modules and even restarting the server does not work. It seems to be just Webmin that is having issues, as querying the zone works. How do I get these zone files to show up in Webmin?