{ nixpkgs ? import <nixpkgs>
}:

import ((nixpkgs {}).fetchFromGitHub {
  owner = "NixOS";
  repo = "nixpkgs";
  rev = "19.03";
  sha256 = "0q2m2qhyga9yq29yz90ywgjbn9hdahs7i8wwlq7b55rdbyiwa5dy";
})