{ nixpkgs ? import <nixpkgs>
}:

import ((nixpkgs {}).fetchFromGitHub {
  owner = "NixOS";
  repo = "nixpkgs";
  rev = "19.03";
  sha256 = "0qixmc228vay4jywf14cg72m1g07ffsl75xg5qrdj70hw9xbd6sg";
})