{
  nixpkgs = builtins.fetchGit {
    url = "https://github.com/nixos/nixpkgs-channels";
    ref = "nixos-19.03";
    rev = "a6598a6c8656557ccd9ac85396dc56e5af8e1135";
  };
  nixpkgs-unstable = builtins.fetchGit {
    url = "https://github.com/nixos/nixpkgs-channels";
    ref = "nixos-unstable";
    rev = "1036dc664169b32613ec11b58cc1740c7511a340";
  };
}