diff --git a/pkgs/by-name/ni/nixfmt-rfc-style/date.txt b/pkgs/by-name/ni/nixfmt-rfc-style/date.txt
new file mode 100644
index 0000000..f4f1f2e
--- /dev/null
+++ b/pkgs/by-name/ni/nixfmt-rfc-style/date.txt
@@ -0,0 +1 @@
+2024-03-01
diff --git a/pkgs/by-name/ni/nixfmt-rfc-style/default.nix b/pkgs/by-name/ni/nixfmt-rfc-style/default.nix
new file mode 100644
index 0000000..e3bb440
--- /dev/null
+++ b/pkgs/by-name/ni/nixfmt-rfc-style/default.nix
@@ -0,0 +1,40 @@
+{
+  haskell,
+  haskellPackages,
+  lib,
+  runCommand,
+  nixfmt-rfc-style,
+  fetchpatch,
+}:
+let
+  inherit (haskell.lib.compose) overrideCabal justStaticExecutables;
+
+  overrides = {
+    version = "unstable-${lib.fileContents ./date.txt}";
+
+    passthru.updateScript = ./update.sh;
+
+    patches = [
+      (fetchpatch {
+        url = "https://github.com/serokell/nixfmt/commit/ca9c8975ed671112fdfce94f2e9e2ad3de480c9a.patch";
+        hash = "sha256-UOSAYahSKBsqPMVcQJ3H26Eg2xpPAsNOjYMI6g+WTYU=";
+      })
+    ];
+
+    maintainers = [ ];
+
+    # These tests can be run with the following command.
+    #
+    # $ nix-build -A nixfmt-rfc-style.tests
+    passthru.tests =
+      runCommand "nixfmt-rfc-style-tests" { nativeBuildInputs = [ nixfmt-rfc-style ]; }
+        ''
+          nixfmt --version > $out
+        '';
+  };
+  raw-pkg = haskellPackages.callPackage ./generated-package.nix { };
+in
+lib.pipe raw-pkg [
+  (overrideCabal overrides)
+  justStaticExecutables
+]
diff --git a/pkgs/by-name/ni/nixfmt-rfc-style/generated-package.nix b/pkgs/by-name/ni/nixfmt-rfc-style/generated-package.nix
new file mode 100644
index 0000000..738b3e5
--- /dev/null
+++ b/pkgs/by-name/ni/nixfmt-rfc-style/generated-package.nix
@@ -0,0 +1,27 @@
+# This file has been autogenerate with cabal2nix.
+# Update via ./update.sh
+{ mkDerivation, base, cmdargs, directory, fetchzip, filepath, lib
+, megaparsec, mtl, parser-combinators, safe-exceptions, scientific
+, text, transformers, unix
+}:
+mkDerivation {
+  pname = "nixfmt";
+  version = "0.5.0";
+  src = fetchzip {
+    url = "https://github.com/piegamesde/nixfmt/archive/2b5ee820690bae64cb4003e46917ae43541e3e0b.tar.gz";
+    sha256 = "1i1jbc1q4gd7fpilwy6s3a583yl5l8d8rlmipygj61mpclg9ihqg";
+  };
+  isLibrary = true;
+  isExecutable = true;
+  libraryHaskellDepends = [
+    base megaparsec mtl parser-combinators scientific text transformers
+  ];
+  executableHaskellDepends = [
+    base cmdargs directory filepath safe-exceptions text unix
+  ];
+  jailbreak = true;
+  homepage = "https://github.com/serokell/nixfmt";
+  description = "An opinionated formatter for Nix";
+  license = lib.licenses.mpl20;
+  mainProgram = "nixfmt";
+}
diff --git a/pkgs/by-name/ni/nixfmt-rfc-style/update.sh b/pkgs/by-name/ni/nixfmt-rfc-style/update.sh
new file mode 100755
index 0000000..c70a6e8
--- /dev/null
+++ b/pkgs/by-name/ni/nixfmt-rfc-style/update.sh
@@ -0,0 +1,33 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p cabal2nix curl jq
+#
+# This script will update the nixfmt-rfc-style derivation to the latest version using
+# cabal2nix.
+
+set -eo pipefail
+
+# This is the directory of this update.sh script.
+script_dir="$( cd "$( dirname "${BASH_SOURCE[0]}" )" >/dev/null 2>&1 && pwd )"
+
+derivation_file="${script_dir}/generated-package.nix"
+date_file="${script_dir}/date.txt"
+
+# This is the latest version of nixfmt-rfc-style branch on GitHub.
+new_version=$(curl --silent https://api.github.com/repos/piegamesde/nixfmt/git/refs/heads/rfc101-style | jq '.object.sha' --raw-output)
+new_date=$(curl --silent https://api.github.com/repos/piegamesde/nixfmt/git/commits/"$new_version" | jq '.committer.date' --raw-output)
+
+echo "Updating nixfmt-rfc-style to version $new_date."
+echo "Running cabal2nix and outputting to ${derivation_file}..."
+
+cat > "$derivation_file" << EOF
+# This file has been autogenerate with cabal2nix.
+# Update via ./update.sh
+EOF
+
+cabal2nix --jailbreak \
+  "https://github.com/piegamesde/nixfmt/archive/${new_version}.tar.gz" \
+  >> "$derivation_file"
+
+date --date="$new_date" -I > "$date_file"
+
+echo "Finished."