diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
index 8132cf8..52adf0f 100644
--- a/.github/workflows/check.yml
+++ b/.github/workflows/check.yml
@@ -12,3 +12,6 @@ jobs:
       - uses: "DeterminateSystems/magic-nix-cache-action@main"
       - name: Flake check
         run: nix develop --command check
+      - name: Check formatting
+        run: |
+          git ls-files '*.nix' | nix develop --command xargs nixpkgs-fmt --check
diff --git a/c-cpp/flake.nix b/c-cpp/flake.nix
index 15e740a..9d3b016 100644
--- a/c-cpp/flake.nix
+++ b/c-cpp/flake.nix
@@ -12,24 +12,25 @@
     in
     {
       devShells = forEachSupportedSystem ({ pkgs }: {
-        default = pkgs.mkShell.override {
-          # Override stdenv in order to change compiler:
-          # stdenv = pkgs.clangStdenv;
-        }
-        {
-          packages = with pkgs; [
-            clang-tools
-            cmake
-            codespell
-            conan
-            cppcheck
-            doxygen
-            gtest
-            lcov
-            vcpkg
-            vcpkg-tool
-          ] ++ (if system == "aarch64-darwin" then [ ] else [ gdb ]);
-        };
+        default = pkgs.mkShell.override
+          {
+            # Override stdenv in order to change compiler:
+            # stdenv = pkgs.clangStdenv;
+          }
+          {
+            packages = with pkgs; [
+              clang-tools
+              cmake
+              codespell
+              conan
+              cppcheck
+              doxygen
+              gtest
+              lcov
+              vcpkg
+              vcpkg-tool
+            ] ++ (if system == "aarch64-darwin" then [ ] else [ gdb ]);
+          };
       });
     };
 }
diff --git a/elixir/flake.lock b/elixir/flake.lock
index f694c77..6add7d4 100644
--- a/elixir/flake.lock
+++ b/elixir/flake.lock
@@ -1,23 +1,5 @@
 {
   "nodes": {
-    "flake-utils": {
-      "inputs": {
-        "systems": "systems"
-      },
-      "locked": {
-        "lastModified": 1710146030,
-        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
-        "type": "github"
-      },
-      "original": {
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "type": "github"
-      }
-    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1719075281,
@@ -34,24 +16,8 @@
     },
     "root": {
       "inputs": {
-        "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs"
       }
-    },
-    "systems": {
-      "locked": {
-        "lastModified": 1681028828,
-        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
-        "owner": "nix-systems",
-        "repo": "default",
-        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-systems",
-        "repo": "default",
-        "type": "github"
-      }
     }
   },
   "root": "root",
diff --git a/elixir/flake.nix b/elixir/flake.nix
index 6b248cd..aa48cc1 100644
--- a/elixir/flake.nix
+++ b/elixir/flake.nix
@@ -1,22 +1,20 @@
 {
   description = "A Nix-flake-based Elixir development environment";
 
-  inputs = {
-    nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1.*.tar.gz";
-
-    flake-utils = {
-      url = "github:numtide/flake-utils";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-  };
-
-  outputs =
-    { self, nixpkgs, flake-utils }:
-    flake-utils.lib.eachDefaultSystem (
-      system:
-      let
-        pkgs = nixpkgs.legacyPackages.${system};
-
+  inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1.*.tar.gz";
+
+  outputs = { self, nixpkgs }:
+    let
+      supportedSystems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
+        pkgs = import nixpkgs {
+          inherit system;
+          overlays = [ self.overlays.default ];
+        };
+      });
+    in
+    {
+      overlays.default = final: prev: rec {
         # documentation
         # https://nixos.org/manual/nixpkgs/stable/#sec-beam
 
@@ -26,7 +24,7 @@
         # erlang = pkgs.beam.interpreters.erlang;
 
         # use latest version of Erlang 27
-        erlang = pkgs.beam.interpreters.erlang_27;
+        erlang = final.beam.interpreters.erlang_27;
 
         # specify exact version of Erlang OTP
         # erlang = pkgs.beam.interpreters.erlang.override {
@@ -37,7 +35,7 @@
         # ==== BEAM packages ====
 
         # all BEAM packages will be compile with your preferred erlang version
-        pkgs-beam = pkgs.beam.packagesWith erlang;
+        pkgs-beam = final.beam.packagesWith erlang;
 
         # ==== Elixir ====
 
@@ -52,49 +50,35 @@
         #   version = "1.17.1";
         #   sha256 = "sha256-a7A+426uuo3bUjggkglY1lqHmSbZNpjPaFpQUXYtW9k=";
         # };
-
-      in
-      {
-        devShells.default = pkgs.mkShell {
-          packages =
-            [
-              # use the Elixr/OTP versions defined above; will also install OTP, mix, hex, rebar3
-              elixir
-
-              # mix needs it for downloading dependencies
-              pkgs.git
-
-              # probably needed for your Phoenix assets
-              pkgs.nodejs_20
-            ]
-            ++
-            # Linux only
-            pkgs.lib.optionals pkgs.stdenv.isLinux (
-              with pkgs;
-              [
-                gigalixir
-                inotify-tools
-                libnotify
-              ]
-            )
-            ++
-              # macOS only
-              pkgs.lib.optionals pkgs.stdenv.isDarwin (
-                with pkgs;
-                [
-                  terminal-notifier
-                  darwin.apple_sdk.frameworks.CoreFoundation
-                  darwin.apple_sdk.frameworks.CoreServices
-                ]
-              );
-
-          # some sane defaults for iex session
-          env = {
-            ERL_INCLUDE_PATH = "${erlang}/lib/erlang/usr/include";
-            ERL_AFLAGS = "+pc unicode -kernel shell_history enabled";
-            ELIXIR_ERL_OPTIONS = "+sssdio 128";
-          };
+      };
+
+      devShells = forEachSupportedSystem ({ pkgs }: {
+        default = pkgs.mkShell {
+          packages = with pkgs; [
+            # use the Elixr/OTP versions defined above; will also install OTP, mix, hex, rebar3
+            elixir
+
+            # mix needs it for downloading dependencies
+            git
+
+            # probably needed for your Phoenix assets
+            nodejs_20
+          ]
+          ++
+          # Linux only
+          pkgs.lib.optionals pkgs.stdenv.isLinux (with pkgs; [
+            gigalixir
+            inotify-tools
+            libnotify
+          ])
+          ++
+          # macOS only
+          pkgs.lib.optionals pkgs.stdenv.isDarwin (with pkgs; [
+            terminal-notifier
+            darwin.apple_sdk.frameworks.CoreFoundation
+            darwin.apple_sdk.frameworks.CoreServices
+          ]);
         };
-      }
-    );
+      });
+    };
 }
diff --git a/python/flake.nix b/python/flake.nix
index c995e07..7f585d2 100644
--- a/python/flake.nix
+++ b/python/flake.nix
@@ -15,9 +15,9 @@
         default = pkgs.mkShell {
           venvDir = ".venv";
           packages = with pkgs; [ python311 ] ++
-            (with pkgs.python311Packages; [ 
+            (with pkgs.python311Packages; [
               pip
-              venvShellHook 
+              venvShellHook
             ]);
         };
       });
diff --git a/r/flake.nix b/r/flake.nix
index da334ef..d18de98 100644
--- a/r/flake.nix
+++ b/r/flake.nix
@@ -21,7 +21,8 @@
       devShells = forEachSupportedSystem ({ pkgs }: {
         default = pkgs.mkShell {
           packages = with pkgs;
-            [ rEnv
+            [
+              rEnv
               pandoc
               texlive.combined.scheme-full
             ];