diff --git a/inventory.json b/inventory.json
index 7e50ba188..af7896845 100644
--- a/inventory.json
+++ b/inventory.json
@@ -5,6 +5,9 @@
       "description": "A nice thing",
       "icon": "./path/to/icon.png",
       "tags": ["1", "2", "3"]
+    },
+    "test-darwin-machine": {
+      "machineClass": "darwin"
     }
   },
   "services": {
diff --git a/lib/build-clan/module.nix b/lib/build-clan/module.nix
index 9f69bf99b..16ca78aff 100644
--- a/lib/build-clan/module.nix
+++ b/lib/build-clan/module.nix
@@ -164,16 +164,18 @@ let
       };
   };
 
-  allMachines = inventory.machines or { } // machines;
+  allMachines = inventoryClass.machines;
 
-  machineClass = lib.mapAttrs (name: _: inventory.machineClass.${name} or "nixos") allMachines;
-
-  configurations = lib.mapAttrs (
-    name: _: moduleSystemConstructor.${machineClass.${name}} { inherit name; }
+  machineClasses = lib.mapAttrs (
+    name: _: inventory.machines.${name}.machineClass or "nixos"
   ) allMachines;
 
-  nixosConfigurations = lib.filterAttrs (name: _: machineClass.${name} == "nixos") configurations;
-  darwinConfigurations = lib.filterAttrs (name: _: machineClass.${name} == "darwin") configurations;
+  configurations = lib.mapAttrs (
+    name: _: moduleSystemConstructor.${machineClasses.${name}} { inherit name; }
+  ) allMachines;
+
+  nixosConfigurations = lib.filterAttrs (name: _: machineClasses.${name} == "nixos") configurations;
+  darwinConfigurations = lib.filterAttrs (name: _: machineClasses.${name} == "darwin") configurations;
 
   # This instantiates NixOS for each system that we support:
   # configPerSystem = <system>.<machine>.nixosConfiguration
@@ -184,7 +186,7 @@ let
       lib.nameValuePair system (
         lib.mapAttrs (
           name: _:
-          moduleSystemConstructor.${machineClass.${name}} {
+          moduleSystemConstructor.${machineClasses.${name}} {
             inherit name system;
             pkgs = pkgsFor.${system};
           }
@@ -199,7 +201,7 @@ let
       lib.nameValuePair system (
         lib.mapAttrs (
           name: _: args:
-          moduleSystemConstructor.${machineClass.${name}} (
+          moduleSystemConstructor.${machineClasses.${name}} (
             args
             // {
               inherit name system;
diff --git a/lib/build-clan/tests.nix b/lib/build-clan/tests.nix
index f87918e7a..875f6e538 100644
--- a/lib/build-clan/tests.nix
+++ b/lib/build-clan/tests.nix
@@ -210,14 +210,16 @@ in
         meta.name = "test";
 
         machines.machine1 = { };
-        machines.machine2 = { };
-        machines.machine3 = { };
-
-        inventory.machineClass.machine2 = "darwin";
-        inventory.machineClass.machine3 = "nixos";
+        inventory.machines.machine2 = {
+          machineClass = "darwin";
+        };
+        inventory.machines.machine3 = {
+          machineClass = "nixos";
+        };
       };
     in
     {
+      inherit result;
       expr = {
         nixos = builtins.attrNames result.nixosConfigurations;
         darwin = builtins.attrNames result.darwinConfigurations;
@@ -241,7 +243,6 @@ in
         meta.name = "test";
 
         machines.machine1.non_existent_option = throw "eval error";
-        inventory.machines.machine1.other_non_existent_option = throw "different eval error";
       };
     in
     {
diff --git a/lib/inventory/build-inventory/interface.nix b/lib/inventory/build-inventory/interface.nix
index 110b3199b..45564f6d9 100644
--- a/lib/inventory/build-inventory/interface.nix
+++ b/lib/inventory/build-inventory/interface.nix
@@ -243,6 +243,19 @@ in
             options = {
               inherit (metaOptionsWith name) name description icon;
 
+              machineClass = lib.mkOption {
+                default = "nixos";
+                type = types.enum [
+                  "nixos"
+                  "darwin"
+                ];
+                description = ''
+                  The module system that should be used to construct the machine
+
+                  Set this to `darwin` for macOS machines
+                '';
+              };
+
               tags = lib.mkOption {
                 description = ''
                   List of tags for the machine.
@@ -278,21 +291,6 @@ in
       );
     };
 
-    machineClass = lib.mkOption {
-      default = { };
-      type = types.attrsOf (
-        types.enum [
-          "nixos"
-          "darwin"
-        ]
-      );
-      description = ''
-        The module system that should be used to construct the machine
-
-        Set this to `darwin` for macOS machines
-      '';
-    };
-
     instances = lib.mkOption {
       # Keep as internal until all de-/serialization issues are resolved
       visible = false;
@@ -366,6 +364,7 @@ in
         else
           lib.warn "Inventory.instances and related features are still under development. Please use with care." v;
     };
+
     services = lib.mkOption {
       description = ''
         Services of the inventory.