GPG check failed in qubes builder

I believe I have followed the steps in the “Qubes ISO building” documentation but I end up getting this error:

Error: GPG check FAILED make[2]: *** [/home/user/qubes-builder/qubes-src/builder-rpm/Makefile-legacy.rpmbuilder:52: dist-build-dep.spec] Error 1 make[1]: *** [Makefile.generic:197: packages] Error 1 make: *** [Makefile:265: core-qubesdb-vm] Error 1

I assume I missed something but I cant figure it out. Any ideas? NO_SIGN=1 is set in the builder.conf file. Is there another setting/configuration I have to do?