diff --git a/nix/sources.json b/nix/sources.json
index e5bb887d..a5251eff 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -5,10 +5,10 @@
         "homepage": "https://nur.nix-community.org/",
         "owner": "nix-community",
         "repo": "NUR",
-        "rev": "5169a012713a35c4ebef6e1f2841a02116bce5e2",
-        "sha256": "050i6vs5v4g809pa4as0ycdiazsiy0rhnan0g85l0x533vkz9k53",
+        "rev": "3c566b681fab5c9f9656bcc2e1a878abd0bfcd5d",
+        "sha256": "096pna6w1bngqh3c5z684a0r9byjd3z8d0q5ff101fxyw0mi6csi",
         "type": "tarball",
-        "url": "https://github.com/nix-community/NUR/archive/5169a012713a35c4ebef6e1f2841a02116bce5e2.tar.gz",
+        "url": "https://github.com/nix-community/NUR/archive/3c566b681fab5c9f9656bcc2e1a878abd0bfcd5d.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "arc-nixexprs": {
@@ -17,10 +17,10 @@
         "homepage": null,
         "owner": "arcnmx",
         "repo": "nixexprs",
-        "rev": "1a6fb812ced3df8686938021e2daa46823f9f7a4",
-        "sha256": "083w8qsqfavnyyc7g8n5c198jksz9c2myp5m82ldlqn00p274yk2",
+        "rev": "7d9b3512297b634fda5f97a0ffb45d757525bb38",
+        "sha256": "1xfckbg0x11c5qd7zd6nvwq11crxli7pxf2h9rryrc77grja3vly",
         "type": "tarball",
-        "url": "https://github.com/arcnmx/nixexprs/archive/1a6fb812ced3df8686938021e2daa46823f9f7a4.tar.gz",
+        "url": "https://github.com/arcnmx/nixexprs/archive/7d9b3512297b634fda5f97a0ffb45d757525bb38.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "home-manager": {
@@ -61,9 +61,8 @@
     },
     "nix-hexchen": {
         "branch": "main",
-        "ref": "main",
         "repo": "https://gitlab.com/hexchen/nixfiles",
-        "rev": "c0cb61737832d3332984b92939eb15e90ed6b8c2",
+        "rev": "2dfbd032f05ad79176a5756cd76dbda4a828e4d8",
         "type": "git"
     },
     "nixos-mailserver": {
@@ -82,10 +81,10 @@
         "homepage": "",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "93de027ee045d0c1fbf13418fb86d86e6309b962",
-        "sha256": "0lz73h01pzcgz8l20k1qawk20g7jcjnrppbxf1wvr8fq21dl4bj1",
+        "rev": "1fe6ed37fd9beb92afe90671c0c2a662a03463dd",
+        "sha256": "1daa0y3p17shn9gibr321vx8vija6bfsb5zd7h4pxdbbwjkfq8n2",
         "type": "tarball",
-        "url": "https://github.com/nixos/nixpkgs/archive/93de027ee045d0c1fbf13418fb86d86e6309b962.tar.gz",
+        "url": "https://github.com/nixos/nixpkgs/archive/1fe6ed37fd9beb92afe90671c0c2a662a03463dd.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgs-mozilla": {
@@ -106,16 +105,16 @@
         "homepage": "",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "1fe6ed37fd9beb92afe90671c0c2a662a03463dd",
-        "sha256": "1daa0y3p17shn9gibr321vx8vija6bfsb5zd7h4pxdbbwjkfq8n2",
+        "rev": "415db954d8c45ee99bfe5fa18c34e57f9b9cb218",
+        "sha256": "0rxlx4xkayc5bxlkrm6fprkgicighcbzmgkzn70gqh356v4qimkq",
         "type": "tarball",
-        "url": "https://github.com/nixos/nixpkgs/archive/1fe6ed37fd9beb92afe90671c0c2a662a03463dd.tar.gz",
+        "url": "https://github.com/nixos/nixpkgs/archive/415db954d8c45ee99bfe5fa18c34e57f9b9cb218.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "pbb-nixfiles": {
         "branch": "main",
         "repo": "https://git.petabyte.dev/petabyteboy/nixfiles.git",
-        "rev": "c3b08fe355d08facf2b2d2f0f96050892242cd38",
+        "rev": "fbb5aebfcc93383089e1f3d1b1cd07a6d3bab39f",
         "type": "git"
     },
     "qyliss-nixlib": {
@@ -132,10 +131,10 @@
         "homepage": null,
         "owner": "arcnmx",
         "repo": "tf-nix",
-        "rev": "f4fe8c91d7048340ac5ff018c70736db4e92ce25",
-        "sha256": "1qjpj0xwwxhc2qj8ciscqz60x7wgsaw72zza61hckh0qc9xdwx6w",
+        "rev": "217a0d1c61da95d0cb91c9f52138743d0dfc6e4e",
+        "sha256": "0fr740nj0c3sldl5f7abrdxlfpr2iz15ghpafmhhrrgvbyh24aq4",
         "type": "tarball",
-        "url": "https://github.com/arcnmx/tf-nix/archive/f4fe8c91d7048340ac5ff018c70736db4e92ce25.tar.gz",
+        "url": "https://github.com/arcnmx/tf-nix/archive/217a0d1c61da95d0cb91c9f52138743d0dfc6e4e.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }
diff --git a/nix/sources.nix b/nix/sources.nix
index cde012b1..1938409d 100644
--- a/nix/sources.nix
+++ b/nix/sources.nix
@@ -6,156 +6,162 @@ 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_file = pkgs: name: spec:
+    let
+      name' = sanitizeName name + "-src";
+    in
+      if spec.builtin or true then
+        builtins_fetchurl { inherit (spec) url sha256; name = name'; }
+      else
+        pkgs.fetchurl { inherit (spec) url sha256; name = name'; };
 
   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;
-      };
+      name' = sanitizeName 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_git = name: spec:
+    let
+      ref =
+        if spec ? ref then spec.ref else
+          if spec ? branch then "refs/heads/${spec.branch}" else
+            if spec ? tag then "refs/tags/${spec.tag}" else
+              abort "In git source '${name}': Please specify `ref`, `tag` or `branch`!";
+    in
+      builtins.fetchGit { url = spec.repo; inherit (spec) rev; inherit 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 ${name} -a type=tarball -a builtin=true'';
+  fetch_builtin-tarball = name: throw
+    ''[${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 ${name} -a type=file -a builtin=true'';
+  fetch_builtin-url = name: throw
+    ''[${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
   #
 
+  # https://github.com/NixOS/nixpkgs/pull/83241/files#diff-c6f540a4f3bfa4b0e8b6bafd4cd54e8bR695
+  sanitizeName = name:
+    (
+      concatMapStrings (s: if builtins.isList s then "-" else s)
+        (
+          builtins.split "[^[:alnum:]+._?=-]+"
+            ((x: builtins.elemAt (builtins.match "\\.*(.*)" x) 0) name)
+        )
+    );
+
   # The set of packages used when specs are fetched using non-builtins.
-  mkPkgs = sources:
+  mkPkgs = sources: system:
     let
       sourcesNixpkgs =
-        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; })
-        { };
+        import (builtins_fetchTarball { inherit (sources.nixpkgs) url sha256; }) { inherit system; };
       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.
-      '';
+    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
+    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 if spec.type == "file" then fetch_file pkgs name spec
+    else if spec.type == "tarball" then fetch_tarball pkgs name spec
+    else if spec.type == "git" then fetch_git name 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}";
+      abort "ERROR: niv spec ${name} has unknown type ${builtins.toJSON spec.type}";
 
   # If the environment variable NIV_OVERRIDE_${name} is set, then use
   # the path directly as opposed to the fetched source.
   replace = name: drv:
     let
-      saneName = stringAsChars
-        (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
+      saneName = stringAsChars (c: if isNull (builtins.match "[a-zA-Z0-9]" c) then "_" else c) name;
       ersatz = builtins.getEnv "NIV_OVERRIDE_${saneName}";
-    in if ersatz == "" then drv else ersatz;
+    in
+      if ersatz == "" then drv else
+        # this turns the string into an actual Nix path (for both absolute and
+        # relative paths)
+        if builtins.substring 0 1 ersatz == "/" then /. + ersatz else /. + builtins.getEnv "PWD" + "/${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.${attr};
-    }) (attrNames set)));
+  mapAttrs = builtins.mapAttrs or (
+    f: set: with builtins;
+    listToAttrs (map (attr: { name = attr; value = f attr set.${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);
+  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));
+  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));
+  concatMapStrings = f: list: concatStrings (map f list);
   concatStrings = builtins.concatStringsSep "";
 
+  # https://github.com/NixOS/nixpkgs/blob/8a9f58a375c401b96da862d969f66429def1d118/lib/attrsets.nix#L331
+  optionalAttrs = cond: as: if cond then as else {};
+
   # 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;
+  builtins_fetchTarball = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchTarball;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchTarball ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      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;
+  builtins_fetchurl = { url, name ? null, sha256 }@attrs:
+    let
+      inherit (builtins) lessThan nixVersion fetchurl;
+    in
+      if lessThan nixVersion "1.12" then
+        fetchurl ({ inherit url; } // (optionalAttrs (!isNull name) { inherit name; }))
+      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;
+    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
+  mkConfig =
+    { sourcesFile ? if builtins.pathExists ./sources.json then ./sources.json else null
+    , sources ? if isNull sourcesFile then {} else builtins.fromJSON (builtins.readFile sourcesFile)
+    , system ? builtins.currentSystem
+    , pkgs ? mkPkgs sources system
     }: rec {
       # The sources, i.e. the attribute set of spec name to spec
       inherit sources;
@@ -164,6 +170,5 @@ let
       inherit pkgs;
     };
 
-in mkSources (mkConfig { }) // {
-  __functor = _: settings: mkSources (mkConfig settings);
-}
+in
+mkSources (mkConfig {}) // { __functor = _: settings: mkSources (mkConfig settings); }