diff --git a/common/development-machine.nix b/common/development-machine.nix
index 35fefac..4c528c1 100644
--- a/common/development-machine.nix
+++ b/common/development-machine.nix
@@ -22,6 +22,18 @@
     valgrind
 
     nodejs_21
+
+    # mps.overrideAttrs (old: {
+    #   pname = "mps";
+    #   version = "1.118.0";
+
+    #   src = fetchFromGitHub {
+    #     owner = "Ravenbrook";
+    #     repo = "mps";
+    #     rev = "refs/tags/release-${version}";
+    #     hash = "sha256-3ql3jWLccgnQHKf23B1en+nJ9rxqmHcWd7aBr93YER0=";
+    #   };
+    # })
   ];
 
   boot.kernel.sysctl."kernel.perf_event_paranoid" = 1;
diff --git a/common/overlays.nix b/common/overlays.nix
new file mode 100644
index 0000000..ee816a0
--- /dev/null
+++ b/common/overlays.nix
@@ -0,0 +1,9 @@
+inputs:
+[
+  (final: prev: {
+    mps-debug = prev.mps.overrideAttrs (old: {
+      pname = old.pname + "-debug";
+      env.NIX_CFLAGS_COMPILE = old.env.NIX_CFLAGS_COMPILE + " -g -DCONFIG_VAR_COOL";
+    });
+  })
+]
diff --git a/flake.lock b/flake.lock
index b8bbb50..42e7464 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1,22 +1,5 @@
 {
   "nodes": {
-    "bashcfg-input": {
-      "flake": false,
-      "locked": {
-        "lastModified": 1704461224,
-        "narHash": "sha256-lbMvlgLwAgAytz/mmOFMYJu40bKGgtYGHWVG9T1Ypos=",
-        "owner": "pestctrl",
-        "repo": "bash-config",
-        "rev": "015ac81d3ee483ff0b3f13c5e9c912cf428dd745",
-        "type": "github"
-      },
-      "original": {
-        "owner": "pestctrl",
-        "ref": "master",
-        "repo": "bash-config",
-        "type": "github"
-      }
-    },
     "emacs-overlay": {
       "inputs": {
         "flake-utils": "flake-utils",
@@ -129,7 +112,6 @@
     },
     "root": {
       "inputs": {
-        "bashcfg-input": "bashcfg-input",
         "emacs-overlay": "emacs-overlay",
         "home-manager": "home-manager",
         "nixos-hardware": "nixos-hardware",
diff --git a/flake.nix b/flake.nix
index 254f30b..c421172 100644
--- a/flake.nix
+++ b/flake.nix
@@ -3,26 +3,26 @@
     nixpkgs.url = "github:nixos/nixpkgs/nixos-23.11";
     update.url = "github:nixos/nixpkgs/nixos-23.11";
     unstable.url = "github:nixos/nixpkgs/nixos-unstable";
-    emacs-overlay = {
-      url = "github:nix-community/emacs-overlay/master";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
+
     nixos-hardware.url = "github:NixOS/nixos-hardware/master";
 
     home-manager = {
       url = "github:nix-community/home-manager/release-23.11";
       inputs.nixpkgs.follows = "nixpkgs";
     };
-    bashcfg-input = {
-      url = "github:pestctrl/bash-config/master";
-      flake = false;
+    emacs-overlay = {
+      url = "github:nix-community/emacs-overlay/master";
+      inputs.nixpkgs.follows = "nixpkgs";
     };
   };
 
   outputs = { self, nixpkgs, update, unstable, home-manager, nixos-hardware, ... }@inputs:
     let
       system = "x86_64-linux";
-      pkgs = nixpkgs.legacyPackages.${system};
+      pkgs = import nixpkgs {
+        inherit system;
+        overlays = import ./common/overlays.nix inputs;
+      };
       mkSystem = h: {
         "${h}" = nixpkgs.lib.nixosSystem {
           inherit system;
@@ -43,9 +43,11 @@
     in {
 
       nixosConfigurations =
-        (nixpkgs.lib.foldr (a: b: a // b) {}
-          (map mkSystem ["NixDawn" "NixFrame"])) // {
-        NixGate = nixpkgs.lib.nixosSystem {
+        (pkgs.lib.foldr (a: b: a // b) {}
+          (map mkSystem ["NixDawn" "NixFrame"]))
+
+        // {
+        NixGate = pkgs.lib.nixosSystem {
           inherit system;
           specialArgs = { inherit inputs; };
           modules = [
@@ -54,7 +56,7 @@
           ];
         };
 
-        NixSentinel = nixpkgs.lib.nixosSystem {
+        NixSentinel = pkgs.lib.nixosSystem {
           inherit system;
           specialArgs = { inherit inputs; };
           modules = [
@@ -63,12 +65,30 @@
           ];
         };
 
-        # nixosConfigurations.LenoNix = nixpkgs.lib.nixosSystem {
+        # LenoNix = nixpkgs.lib.nixosSystem {
         #   system = "x86_64-linux";
         #   modules = [ ./hosts/NixFrame/configuration.nix ];
         # };
       };
 
+      devShells."${system}" = {
+        default = pkgs.mkShell {
+          # packages = with pkgs; [mps-debug];
+          # nativeBuildInputs = with pkgs; [ mps-debug ] ++ pkgs.emacs.nativeBuildInputs;
+          # buildInputs = pkgs.emacs.buildInputs;
+          packages = with pkgs; [ mps-debug ];
+          inputsFrom = with pkgs; [ emacs ];
+
+          shellHook = ''
+            export MPS_LIB="${pkgs.mps-debug}/lib"
+            export MPS_INC="${pkgs.mps-debug}/include"
+            echo "MPS debug environment!"
+            echo "MPS_LIB = $MPS_LIB"
+            echo "MPS_INC = $MPS_INC"
+          '';
+        };
+      };
+
       homeConfigurations."benson" = home-manager.lib.homeManagerConfiguration {
         inherit pkgs;
         extraSpecialArgs = { inherit inputs; };