Emacs Doesn't Build

unpacking channels...
building Nix...
building the system configuration...
unpacking 'https://github.com/NixOS/nixpkgs-channels/archive/nixos-unstable-small.tar.gz'...
error: Package ‘emacs-with-packages-27.0.50-git’ in /nix/store/l338j8w0xpmn9vii30sdl2wd1l10jfmr-nixpkgs-18.09.2574.a7e559a5504/nixpkgs/pkgs/applications/editors/emacs/default.nix:112 is not supported on ‘x86_64-linux’, refusing to evaluate.

a) For `nixos-rebuild` you can set
  { nixpkgs.config.allowUnsupportedSystem = true; }
in configuration.nix to override this.

b) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
  { allowUnsupportedSystem = true; }
to ~/.config/nixpkgs/config.nix.

(use '--show-trace' to show detailed location information)