OS X 10.12.16: “URLs with the type ‘afp:’ are not supported”

I am mounting an AFP volume hosted on a FreeBSD server using netatalk. I am able to successfully mount the volume using mount_afp. However, I am mounting it for the purposes of Time Machine, and it seems that unfortunately mount_afp changes the permissions of the mount directory to 700, root:wheel so that the user is unable to access it.

So I am trying to mount the volume normally from Finder, unsuccessfully, with the above error code.

The URL I am using to mount it is afp://user:pass@server/VolumeName