diff --git a/lib/default.nix b/lib/default.nix
index 7ea118d51..857a8d14b 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -43,6 +43,8 @@ lib.fix (clanLib: {
   inventory = clanLib.callLib ./inventory { };
   modules = clanLib.callLib ./inventory/frontmatter { };
   test = clanLib.callLib ./test { };
+  # Custom types
+  types = clanLib.callLib ./types { };
 
   # Plain imports.
   introspection = import ./introspection { inherit lib; };
diff --git a/lib/flake-module.nix b/lib/flake-module.nix
index bb4e91c99..abf55216a 100644
--- a/lib/flake-module.nix
+++ b/lib/flake-module.nix
@@ -11,6 +11,7 @@ rec {
     ./introspection/flake-module.nix
     ./inventory/flake-module.nix
     ./jsonschema/flake-module.nix
+    ./types/flake-module.nix
   ];
   flake.clanLib = import ./default.nix {
     inherit lib inputs self;
diff --git a/lib/types/default.nix b/lib/types/default.nix
new file mode 100644
index 000000000..868a83541
--- /dev/null
+++ b/lib/types/default.nix
@@ -0,0 +1,28 @@
+{ lib, ... }:
+{
+  uniqueDeferredSerializableModule = lib.fix (
+    self:
+    # Essentially the "raw" type, but with a custom name and check
+    lib.mkOptionType {
+      name = "deferredModule";
+      description = "deferred module that has custom check and merge behavior";
+      descriptionClass = "noun";
+      # Unfortunately, tryEval doesn't catch JSON errors
+      check = value: lib.seq (builtins.toJSON value) true;
+      merge = lib.options.mergeUniqueOption {
+        message = "------";
+        merge = loc: defs: {
+          imports = map (
+            def: lib.setDefaultModuleLocation "${def.file}, via option ${lib.showOption loc}" def.value
+          ) defs;
+        };
+      };
+      functor = {
+        inherit (self) name;
+        type = self;
+        # Non mergable type
+        binOp = _a: _b: null;
+      };
+    }
+  );
+}
diff --git a/lib/types/flake-module.nix b/lib/types/flake-module.nix
new file mode 100644
index 000000000..2b75953c5
--- /dev/null
+++ b/lib/types/flake-module.nix
@@ -0,0 +1,25 @@
+{ self, inputs, ... }:
+{
+  perSystem =
+    { ... }:
+    let
+      # Module that contains the tests
+      # This module adds:
+      # - legacyPackages.<system>.eval-tests-hello-world
+      # - checks.<system>.eval-tests-hello-world
+      test-types-module = (
+        self.clanLib.test.flakeModules.makeEvalChecks {
+          module = throw "";
+          inherit self inputs;
+          testName = "types";
+          tests = ./tests.nix;
+          # Optional arguments passed to the test
+          testArgs = { };
+        }
+      );
+    in
+    {
+      imports = [ test-types-module ];
+      legacyPackages.xxx = { };
+    };
+}
diff --git a/lib/types/tests.nix b/lib/types/tests.nix
new file mode 100644
index 000000000..268292356
--- /dev/null
+++ b/lib/types/tests.nix
@@ -0,0 +1,41 @@
+{ lib, clanLib, ... }:
+let
+  evalSettingsModule =
+    m:
+    lib.evalModules {
+      modules = [
+        {
+          options.foo = lib.mkOption {
+            type = clanLib.types.uniqueDeferredSerializableModule;
+          };
+        }
+        m
+      ];
+    };
+in
+{
+  test_1 =
+    let
+      eval = evalSettingsModule {
+        foo = { };
+      };
+    in
+    {
+      inherit eval;
+      expr = eval.config.foo;
+      expected = {
+        # Foo has imports
+        # This can only ever be one module due to the type of foo
+        imports = [
+          {
+            # This is the result of 'setDefaultModuleLocation'
+            # Which also returns exactly one module
+            _file = "<unknown-file>, via option foo";
+            imports = [
+              { }
+            ];
+          }
+        ];
+      };
+    };
+}