Problem with rustup installing stable-x86_64-unknown-linux-musl: "error reading rustc version"

A program I like using, creates binaries compiled using musl for it’s updates,
so it makes me want to use that as well, but for whatever reason,
I can not get the rustup toolchain support to work.

$ rustup toolchain add stable-x86_64-unknown-linux-musl
warning: toolchain 'stable-x86_64-unknown-linux-musl' may not be able to run on this system.
warning: If you meant to build software to target that platform, perhaps try `rustup target add x86_64-unknown-linux-musl` instead?
info: syncing channel updates for 'stable-x86_64-unknown-linux-musl'

  stable-x86_64-unknown-linux-musl unchanged - (error reading rustc version)