diff --git a/flake.nix b/flake.nix
index f54a535..13d71ef 100644
--- a/flake.nix
+++ b/flake.nix
@@ -10,6 +10,7 @@
       atauPkgs = {
         atau-wallpapers = pkgs.callPackage ./atau-wallpapers/default.nix { };
         theme-platinum9 = pkgs.callPackage ./theme-platinum9/default.nix { };
+        gtk-theme-mac-os-9 = pkgs.callPackage ./gtk-theme-mac-os-9 { };
       };
     in
     {
@@ -17,6 +18,8 @@
         default = atauPkgs.theme-platinum9;
       } // atauPkgs;
 
-      overlays.default = final: prev: atauPkgs;
+      overlays.default = final: prev: {
+        atau-pkgs = atauPkgs;
+      };
     };
 }
diff --git a/gtk-theme-mac-os-9/default.nix b/gtk-theme-mac-os-9/default.nix
new file mode 100644
index 0000000..b1f6ad0
--- /dev/null
+++ b/gtk-theme-mac-os-9/default.nix
@@ -0,0 +1,29 @@
+{ lib, stdenv }:
+
+stdenv.mkDerivation rec {
+  name = "gtk-theme-mac-os-9";
+  pname = name;
+  version = "ca8a5d2a3fb1976cf904133574a3d0022ac2cf71";
+
+  src = fetchGit {
+    url = "https://github.com/B00merang-Project/Mac-OS-9.git";
+    rev = version;
+  };
+
+  installPhase = ''
+    runHook preInstall
+
+    # Install themes
+    mkdir -p "$out/share/themes/Mac-OS-9"
+    mv * "$out/share/themes/Mac-OS-9"
+
+    runHook postInstall
+  '';
+
+  meta = with lib; {
+    homepage = "https://github.com/B00merang-Project/Mac-OS-9";
+    description = "The classic look of Mac OS 9, now for GTK 3 desktops";
+    platforms = platforms.unix;
+    maintainers = with maintainers; [ atau ];
+  };
+}