diff --git a/.drone.yml b/.drone.yml
index 5003282..e613092 100644
--- a/.drone.yml
+++ b/.drone.yml
@@ -17,7 +17,7 @@ steps:
       NETLIFY_AUTH_TOKEN:
         from_secret: netlify_auth_token
     commands:
-      - nix-shell --run "netlify deploy --prod -d $(readlink -f result)"
+      - nix-shell -I nixpkgs=./pkgs.nix --run "netlify deploy --prod -d $(readlink -f result)"
 
 node:
   nix: 1
diff --git a/default.nix b/default.nix
index 9c10edd..36f29dc 100644
--- a/default.nix
+++ b/default.nix
@@ -1,14 +1,8 @@
 let
-  pkgs = import ./nixpkgs.nix {};
+  sources = import ./nix/sources.nix;
+  pkgs = import sources.nixpkgs {};
 
-  # reproducible source
-  gitignoreSrc = pkgs.fetchFromGitHub {
-    owner = "hercules-ci";
-    repo = "gitignore";
-    rev = "c4662e662462e7bf3c2a968483478a665d00e717";
-    sha256 = "sha256:1npnx0h6bd0d7ql93ka7azhj40zgjp815fw2r6smg8ch9p7mzdlx";
-  };
-  inherit (import gitignoreSrc { inherit (pkgs) lib; }) gitignoreSource;
+  inherit (import sources.gitignore { inherit (pkgs) lib; }) gitignoreSource;
 
   python = (pkgs.python38.withPackages (ps: with ps; [
     CommonMark
@@ -36,7 +30,6 @@ pkgs.stdenv.mkDerivation {
   name = "presis";
 
   nativeBuildInputs = [
-    pkgs.netlify-cli
     python
     texlive
   ];
diff --git a/nix/sources.json b/nix/sources.json
new file mode 100644
index 0000000..3fb6420
--- /dev/null
+++ b/nix/sources.json
@@ -0,0 +1,26 @@
+{
+    "gitignore": {
+        "branch": "master",
+        "description": "Nix function for filtering local git sources",
+        "homepage": "",
+        "owner": "hercules-ci",
+        "repo": "gitignore",
+        "rev": "c4662e662462e7bf3c2a968483478a665d00e717",
+        "sha256": "1npnx0h6bd0d7ql93ka7azhj40zgjp815fw2r6smg8ch9p7mzdlx",
+        "type": "tarball",
+        "url": "https://github.com/hercules-ci/gitignore/archive/c4662e662462e7bf3c2a968483478a665d00e717.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "nixpkgs": {
+        "branch": "release-20.09",
+        "description": "Nix Packages collection",
+        "homepage": "",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "99f8282a65821f148df596ba389606e732eaf99d",
+        "sha256": "1mm4j1vjs875yzv03plng43ivny0qm09hxpn0if8g9vc849rwc2g",
+        "type": "tarball",
+        "url": "https://github.com/NixOS/nixpkgs/archive/99f8282a65821f148df596ba389606e732eaf99d.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    }
+}
diff --git a/nix/sources.nix b/nix/sources.nix
new file mode 100644
index 0000000..b64b8f8
--- /dev/null
+++ b/nix/sources.nix
@@ -0,0 +1,148 @@
+# This file has been generated by Niv.
+
+let
+
+  #
+  # The fetchers. fetch_<type> fetches specs of type <type>.
+  #
+
+  fetch_file = pkgs: spec:
+    if spec.builtin or true then
+      builtins_fetchurl { inherit (spec) url sha256; }
+    else
+      pkgs.fetchurl { inherit (spec) url sha256; };
+
+  fetch_tarball = pkgs: name: spec:
+    let
+      ok = str: ! builtins.isNull (builtins.match "[a-zA-Z0-9+-._?=]" str);
+      # sanitize the name, though nix will still fail if name starts with period
+      name' = stringAsChars (x: if ! ok x then "-" else x) "${name}-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchTarball { name = name'; inherit (spec) url sha256; }
+      else
+        pkgs.fetchzip { name = name'; inherit (spec) url sha256; };
+
+  fetch_git = spec:
+    builtins.fetchGit { url = spec.repo; inherit (spec) rev ref; };
+
+  fetch_local = spec: spec.path;
+
+  fetch_builtin-tarball = name: throw
+    ''[${name}] The niv type "builtin-tarball" is deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=tarball -a builtin=true'';
+
+  fetch_builtin-url = name: throw
+    ''[${name}] The niv type "builtin-url" will soon be deprecated. You should instead use `builtin = true`.
+        $ niv modify ${name} -a type=file -a builtin=true'';
+
+  #
+  # Various helpers
+  #
+
+  # The set of packages used when specs are fetched using non-builtins.
+  mkPkgs = sources:
+    let
+      sourcesNixpkgs =
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) {};
+      hasNixpkgsPath = builtins.any (x: x.prefix == "nixpkgs") builtins.nixPath;
+      hasThisAsNixpkgsPath = <nixpkgs> == ./.;
+    in
+      if builtins.hasAttr "nixpkgs" sources
+      then sourcesNixpkgs
+      else if hasNixpkgsPath && ! hasThisAsNixpkgsPath then
+        import <nixpkgs> {}
+      else
+        abort
+          ''
+            Please specify either <nixpkgs> (through -I or NIX_PATH=nixpkgs=...) or
+            add a package called "nixpkgs" to your sources.json.
+          '';
+
+  # The actual fetching function.
+  fetch = pkgs: name: spec:
+
+    if ! builtins.hasAttr "type" spec then
+      abort "ERROR: niv spec ${name} does not have a 'type' attribute"
+    else if spec.type == "file" then fetch_file pkgs spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
+    else if spec.type == "git" then fetch_git spec
+    else if spec.type == "local" then fetch_local spec
+    else if spec.type == "builtin-tarball" then fetch_builtin-tarball name
+    else if spec.type == "builtin-url" then fetch_builtin-url name
+    else
+      abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
+
+  # If the environment variable NIV_OVERRIDE_${name} is set, then use
+  # the path directly as opposed to the fetched source.
+  replace = name: drv:
+    let
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
+    in
+      if ersatz == "" then drv else ersatz;
+
+  # Ports of functions for older nix versions
+
+  # a Nix version of mapAttrs if the built-in doesn't exist
+  mapAttrs = builtins.mapAttrs or (
+    f: set: with builtins;
+    listToAttrs (map (attr: { name = attr; value = f attr set.${attr}; }) (attrNames set))
+  );
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/lists.nix#L295
+  range = first: last: if first > last then [] else builtins.genList (n: first + n) (last - first + 1);
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L257
+  stringToCharacters = s: map (p: builtins.substring p 1 s) (range 0 (builtins.stringLength s - 1));
+
+  # https://github.com/NixOS/nixpkgs/blob/0258808f5744ca980b9a1f24fe0b1e6f0fecee9c/lib/strings.nix#L269
+  stringAsChars = f: s: concatStrings (map f (stringToCharacters s));
+  concatStrings = builtins.concatStringsSep "";
+
+  # fetchTarball version that is compatible between all the versions of Nix
+  builtins_fetchTarball = { url, name, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball { inherit name url; }
+      else
+        fetchTarball attrs;
+
+  # fetchurl version that is compatible between all the versions of Nix
+  builtins_fetchurl = { url, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchurl;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchurl { inherit url; }
+      else
+        fetchurl attrs;
+
+  # Create the final "sources" from the config
+  mkSources = config:
+    mapAttrs (
+      name: spec:
+        if builtins.hasAttr "outPath" spec
+        then abort
+          "The values in sources.json should not have an 'outPath' attribute"
+        else
+          spec // { outPath = replace name (fetch config.pkgs name spec); }
+    ) config.sources;
+
+  # The "config" used by the fetchers
+  mkConfig =
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
+    , pkgs ? mkPkgs sources
+    }: rec {
+      # The sources, i.e. the attribute set of spec name to spec
+      inherit sources;
+
+      # The "pkgs" (evaluated nixpkgs) to use for e.g. non-builtin fetchers
+      inherit pkgs;
+    };
+
+in
+mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }
diff --git a/nixpkgs.nix b/nixpkgs.nix
deleted file mode 100644
index 473af12..0000000
--- a/nixpkgs.nix
+++ /dev/null
@@ -1,4 +0,0 @@
-import (fetchTarball {
-  url = "https://github.com/NixOS/nixpkgs/archive/24c9b05ac53e422f1af81a156f1fd58499eb27fb.tar.gz";
-  sha256 = "1aw5zxd91rzvvzqk8zi5qrnkjsgf4nv77pa3jbpsymhpwr0gj5i3";
-})
diff --git a/pkgs.nix b/pkgs.nix
new file mode 100644
index 0000000..4ccc1ca
--- /dev/null
+++ b/pkgs.nix
@@ -0,0 +1 @@
+import (import ./nix/sources.nix).nixpkgs
diff --git a/shell.nix b/shell.nix
index 95da550..d4cf217 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1 +1,9 @@
-import ./default.nix
+let
+  pkgs = import (import ./nix/sources.nix).nixpkgs {};
+in
+(import ./default.nix).overrideAttrs(o: o // {
+  nativeBuildInputs = o.nativeBuildInputs ++ (with pkgs; [
+    bash
+    netlify-cli
+  ]);
+})