diff --git a/README.md b/README.md
index 09109f3..2eb5721 100644
--- a/README.md
+++ b/README.md
@@ -17,14 +17,16 @@ nix run
     - X1 Carbon: https://www.srid.ca/x1c7-install
     - Windows (via WSL): https://github.com/nix-community/NixOS-WSL
   - Clone this repo at `/etc/nixos`
-  - Edit `flake.nix` and add your Linux's hostname in the `nixosConfigurations` set, as well as update `userName`.
+  - Edit `flake.nix` and 
+    - add your Linux's hostname in the `nixosConfigurations` set, as well as
+    - update `myUserName`.
   - Run `nix run`. That's it. Re-open your shell.
 - macOS: 
     - Install Nix normally (multi-user)
     - Install [nix-darwin](https://github.com/LnL7/nix-darwin) 
         - This will create a `~/.nixpkgs/darwin-configuration.nix`, but we do not need that. 
     - Clone this repo anywhere
-    - Edit `flake.nix` to update `userName`.
+    - Edit `flake.nix` to update `myUserName`.
     - Run `nix run`.[^cleanup] That's it. Re-open your shell.
 
 [^cleanup]: You might have to `rm -rf /etc/nix/nix.conf`, so our flake.nix can do its thing.
diff --git a/config.nix b/config.nix
new file mode 100644
index 0000000..ce9c0c9
--- /dev/null
+++ b/config.nix
@@ -0,0 +1,9 @@
+{ config, lib, ... }:
+{
+  options = {
+    myUserName = lib.mkOption {
+      type = lib.types.str;
+      description = "The canonical (only) user to add to all systems.";
+    };
+  };
+}
diff --git a/flake.nix b/flake.nix
index 4bf7dc1..67ecc2f 100644
--- a/flake.nix
+++ b/flake.nix
@@ -33,6 +33,7 @@
     inputs.flake-parts.lib.mkFlake { inherit (inputs) self; } {
       systems = [ "x86_64-linux" "aarch64-darwin" ];
       imports = [
+        ./config.nix
         ./home
         ./nixos
         ./nix-darwin
@@ -44,39 +45,36 @@
         };
         formatter = pkgs.nixpkgs-fmt;
       };
-      flake =
-        let
-          userName = "srid";
-        in
-        {
-          # Configurations for Linux (NixOS) systems
-          nixosConfigurations = {
-            # My Linux development computer (on Hetzner)
-            pinch = self.lib.mkLinuxSystem userName
-              [
-                ./systems/hetzner/ax41.nix
-                ./nixos/server/harden.nix
+      myUserName = "srid";
+      flake = {
+        # Configurations for Linux (NixOS) systems
+        nixosConfigurations = {
+          # My Linux development computer (on Hetzner)
+          pinch = self.lib.mkLinuxSystem
+            [
+              ./systems/hetzner/ax41.nix
+              ./nixos/server/harden.nix
 
-                # Temporarily sharing with Uday.
-                {
-                  users.users.uday.isNormalUser = true;
-                  home-manager.users."uday" = {
-                    imports = [
-                      self.homeModules.common-linux
-                      (import ./home/git.nix {
-                        userName = "Uday Kiran";
-                        userEmail = "udaycruise2903@gmail.com";
-                      })
-                    ];
-                  };
-                }
-              ];
-          };
-
-          # Configurations for macOS systems (using nix-darwin)
-          darwinConfigurations = {
-            default = self.lib-darwin.mkMacosSystem userName;
-          };
+              # Temporarily sharing with Uday.
+              {
+                users.users.uday.isNormalUser = true;
+                home-manager.users."uday" = {
+                  imports = [
+                    self.homeModules.common-linux
+                    (import ./home/git.nix {
+                      userName = "Uday Kiran";
+                      userEmail = "udaycruise2903@gmail.com";
+                    })
+                  ];
+                };
+              }
+            ];
         };
+
+        # Configurations for macOS systems (using nix-darwin)
+        darwinConfigurations = {
+          default = self.lib-darwin.mkMacosSystem;
+        };
+      };
     };
 }
diff --git a/nix-darwin/default.nix b/nix-darwin/default.nix
index 6b7134b..1247c64 100644
--- a/nix-darwin/default.nix
+++ b/nix-darwin/default.nix
@@ -1,4 +1,4 @@
-{ self, inputs, ... }:
+{ self, inputs, config, ... }:
 {
   # Configuration common to all macOS systems
   flake = {
@@ -20,7 +20,7 @@
         self.darwinModules.home
       ];
     };
-    lib-darwin.mkMacosSystem = userName: inputs.darwin.lib.darwinSystem rec {
+    lib-darwin.mkMacosSystem = inputs.darwin.lib.darwinSystem rec {
       system = "aarch64-darwin";
       specialArgs = {
         inherit inputs system;
@@ -30,7 +30,7 @@
         self.darwinModules.default
         ../systems/darwin.nix
         {
-          home-manager.users.${userName} = { pkgs, ... }: {
+          home-manager.users.${config.myUserName} = { pkgs, ... }: {
             imports = [
               self.homeModules.common-darwin
               ../home/shellcommon.nix
diff --git a/nixos/default.nix b/nixos/default.nix
index e045d34..8e13fcc 100644
--- a/nixos/default.nix
+++ b/nixos/default.nix
@@ -1,4 +1,4 @@
-{ self, inputs, ... }:
+{ self, inputs, config, ... }:
 {
   # Configuration common to all Linux systems
   flake = {
@@ -28,14 +28,14 @@
         ];
     };
 
-    lib.mkLinuxSystem = userName: extraModules: inputs.nixpkgs.lib.nixosSystem rec {
+    lib.mkLinuxSystem = extraModules: inputs.nixpkgs.lib.nixosSystem rec {
       system = "x86_64-linux";
       # Arguments to pass to all modules.
       specialArgs = { inherit system inputs; };
       modules = [
         self.nixosModules.default
         {
-          home-manager.users.${userName} = { pkgs, ... }: {
+          home-manager.users.${config.myUserName} = { pkgs, ... }: {
             imports = [
               self.homeModules.common-linux
               ../home/shellcommon.nix