diff --git a/src/Updux.ts b/src/Updux.ts
index b9358a9..d35b81c 100644
--- a/src/Updux.ts
+++ b/src/Updux.ts
@@ -116,6 +116,7 @@ export default class Updux<
             this.initial,
             this.#localMutations,
             this.#defaultMutation,
+            this.#subduxes,
         ) as any as (
             state: undefined | typeof this.initial,
             action: Action,
diff --git a/src/buildUpreducer.todo b/src/buildUpreducer.todo
deleted file mode 100644
index 39672ac..0000000
--- a/src/buildUpreducer.todo
+++ /dev/null
@@ -1,45 +0,0 @@
-import u from 'updeep';
-import { mapValues } from 'lodash-es';
-
-export function buildUpreducer(
-    initial,
-    mutations,
-    subduxes = {},
-    wrapper = undefined,
-) {
-    const subReducers =
-        Object.keys(subduxes).length > 0
-            ? mapValues(subduxes, ({ upreducer }) => upreducer)
-            : null;
-
-    const upreducer = (action) => (state) => {
-        if (!action?.type)
-            throw new Error('upreducer called with a bad action');
-
-        let newState = state ?? initial;
-
-        if (subReducers) {
-            if (subduxes['*']) {
-                newState = u.updateIn(
-                    '*',
-                    subduxes['*'].upreducer(action),
-                    newState,
-                );
-            } else {
-                const update = mapValues(subReducers, (upReducer) =>
-                    upReducer(action),
-                );
-
-                newState = u(update, newState);
-            }
-        }
-
-        const a = mutations[action.type] || mutations['+'];
-
-        if (!a) return newState;
-
-        return a(action.payload, action)(newState);
-    };
-
-    return wrapper ? wrapper(upreducer) : upreducer;
-}
diff --git a/src/mutations.test.todo b/src/mutations.test.todo
deleted file mode 100644
index 7e72b34..0000000
--- a/src/mutations.test.todo
+++ /dev/null
@@ -1,48 +0,0 @@
-import schema from 'json-schema-shorthand';
-import u from 'updeep';
-
-import { action } from './actions.js';
-
-import { Updux, dux } from './Updux.js';
-
-test('mutation of a subdux', async () => {
-    const bar = dux({
-        actions: {
-            baz: null,
-        },
-    });
-    bar.setMutation('baz', () => (state) => ({ ...state, x: 1 }));
-
-    const foo = dux({
-        subduxes: { bar },
-    });
-
-    const store = foo.createStore();
-    store.dispatch.baz();
-    expect(store.getState()).toMatchObject({ bar: { x: 1 } });
-});
-
-test('strings and generators', async () => {
-    const actionA = action('a');
-
-    const foo = dux({
-        actions: {
-            b: null,
-            a: actionA,
-        },
-    });
-
-    // as a string and defined
-    expect(() => foo.setMutation('a', () => {})).not.toThrow();
-
-    // as a generator and defined
-    expect(() => foo.setMutation(actionA, () => {})).not.toThrow();
-
-    // as a string, not defined
-    expect(() => foo.setMutation('c', () => {})).toThrow();
-
-    foo.setMutation(action('d'), () => {});
-
-    expect(foo.actions.d).toBeTypeOf('function');
-});
-
diff --git a/src/mutations.test.ts b/src/mutations.test.ts
index 09c3000..5858b63 100644
--- a/src/mutations.test.ts
+++ b/src/mutations.test.ts
@@ -1,6 +1,6 @@
 import { test, expect } from 'vitest';
 
-import Updux from './index.js';
+import Updux, { createAction } from './index.js';
 
 test('set a mutation', () => {
     const dux = new Updux({
@@ -53,3 +53,28 @@ test('default mutation', () => {
     expect(dux.reducer(undefined, { type: 'foo' })).toEqual('got it');
     expect(dux.reducer(undefined, { type: 'bar' })).toEqual('bar');
 });
+
+test('mutation of a subdux', () => {
+    const baz = createAction('baz');
+    const noop = createAction('noop');
+    const stopit = createAction('stopit');
+
+    const bar = new Updux({
+        initial: 0,
+        actions: {
+            baz,
+            stopit,
+        },
+    });
+    bar.addMutation(baz, () => () => 1);
+    bar.addMutation(stopit, () => () => 2);
+
+    const foo = new Updux({
+        subduxes: { bar },
+    });
+    foo.addMutation(stopit, () => (state) => state, true);
+
+    expect(foo.reducer(undefined, noop())).toHaveProperty('bar', 0);
+    expect(foo.reducer(undefined, baz())).toHaveProperty('bar', 1);
+    expect(foo.reducer(undefined, stopit())).toHaveProperty('bar', 0);
+});
diff --git a/src/reducer.ts b/src/reducer.ts
index 12b431c..9ca2571 100644
--- a/src/reducer.ts
+++ b/src/reducer.ts
@@ -16,8 +16,7 @@ export function buildReducer(
     defaultMutation?: Omit<MutationCase, 'matcher'>,
     subduxes: Record<string, Dux> = {},
 ) {
-    // const subReducers =
-    //         ? R.mapValues(subduxes, R.prop('reducer'));
+    const subReducers = R.mapValues(subduxes, R.prop('reducer'));
 
     // TODO matcherMutation
     // TODO defaultMutation
@@ -48,6 +47,16 @@ export function buildReducer(
             )(state);
         }
 
+        if (!terminal && Object.keys(subduxes).length > 0) {
+            // subduxes
+            state = R.merge(
+                state,
+                R.mapValues(subReducers, (reducer, slice) =>
+                    (reducer as any)(state[slice], action),
+                ),
+            );
+        }
+
         return state;
     };