diff --git a/lib/modules.nix b/lib/modules.nix
index 92ddc8c5bc70..2468b6fbdd22 100644
--- a/lib/modules.nix
+++ b/lib/modules.nix
@@ -62,6 +62,8 @@ rec {
       ‘type’: A module system type representing the module set as a submodule,
             to be extended by configuration from the containing module set.
 
+            This is also available as the module argument ‘moduleType’.
+
       ‘extendModules’: A function similar to ‘evalModules’ but building on top
             of the module set. Its arguments, ‘modules’ and ‘specialArgs’ are
             added to the existing values.
@@ -74,6 +76,8 @@ rec {
             override existing configuration fundamentally requires a new
             fixpoint to be constructed.
 
+            This is also available as a module argument.
+
       ‘_module’: A portion of the configuration tree which is elided from
             ‘config’. It contains some values that are mostly internal to the
             module system implementation.
@@ -146,6 +150,7 @@ rec {
         config = {
           _module.args = {
             inherit extendModules;
+            moduleType = type;
           } // args;
         };
       };
diff --git a/lib/tests/modules.sh b/lib/tests/modules.sh
index aba3f08122f5..2f36d6107ca4 100755
--- a/lib/tests/modules.sh
+++ b/lib/tests/modules.sh
@@ -281,6 +281,11 @@ checkConfigError 'A definition for option .fun.\[function body\]. is not of type
 checkConfigOutput "b a" config.result ./functionTo/list-order.nix
 checkConfigOutput "a c" config.result ./functionTo/merging-attrs.nix
 
+# moduleType
+checkConfigOutput "a b" config.resultFoo ./declare-variants.nix ./define-variant.nix
+checkConfigOutput "a y z" config.resultFooBar ./declare-variants.nix ./define-variant.nix
+checkConfigOutput "a b c" config.resultFooFoo ./declare-variants.nix ./define-variant.nix
+
 cat <<EOF
 ====== module tests ======
 $pass Pass
diff --git a/lib/tests/modules/declare-variants.nix b/lib/tests/modules/declare-variants.nix
new file mode 100644
index 000000000000..3ed6fa689e21
--- /dev/null
+++ b/lib/tests/modules/declare-variants.nix
@@ -0,0 +1,9 @@
+{ lib, moduleType, ... }:
+let inherit (lib) mkOption types;
+in
+{
+  options.variants = mkOption {
+    type = types.lazyAttrsOf moduleType;
+    default = {};
+  };
+}
diff --git a/lib/tests/modules/define-variant.nix b/lib/tests/modules/define-variant.nix
new file mode 100644
index 000000000000..423cb0e37cb5
--- /dev/null
+++ b/lib/tests/modules/define-variant.nix
@@ -0,0 +1,22 @@
+{ config, lib, ... }:
+let inherit (lib) types mkOption attrNames;
+in
+{
+  options = {
+    attrs = mkOption { type = types.attrsOf lib.types.int; };
+    result = mkOption { };
+    resultFoo = mkOption { };
+    resultFooBar = mkOption { };
+    resultFooFoo = mkOption { };
+  };
+  config = {
+    attrs.a = 1;
+    variants.foo.attrs.b = 1;
+    variants.bar.attrs.y = 1;
+    variants.foo.variants.bar.attrs.z = 1;
+    variants.foo.variants.foo.attrs.c = 3;
+    resultFoo = lib.concatMapStringsSep " " toString (attrNames config.variants.foo.attrs);
+    resultFooBar = lib.concatMapStringsSep " " toString (attrNames config.variants.foo.variants.bar.attrs);
+    resultFooFoo = lib.concatMapStringsSep " " toString (attrNames config.variants.foo.variants.foo.attrs);
+  };
+}