diff --git a/src/Updux.ts b/src/Updux.ts
index 20221a2..d275700 100644
--- a/src/Updux.ts
+++ b/src/Updux.ts
@@ -8,23 +8,16 @@ import {
 import {
     configureStore,
     Reducer,
-    createAction,
     ActionCreator,
-    PrepareAction,
-    ActionCreatorWithPayload,
     ActionCreatorWithoutPayload,
     ActionCreatorWithPreparedPayload,
 } from '@reduxjs/toolkit';
-import { withPayload } from './actions.js';
-import { AggregateActions, Dux, UnionToIntersection } from './types.js';
+import { AggregateActions, Dux } from './types.js';
 import { buildActions } from './buildActions.js';
-
-type AggregateState<L> = L;
+import { buildInitial, AggregateState } from './initial.js';
 
 type MyActionCreator = { type: string } & ((...args: any) => any);
 
-type F = null extends any ? 'u' : 'n';
-
 type ResolveAction<
     ActionType extends string,
     ActionArg extends any,
@@ -59,33 +52,37 @@ export default class Updux<
     T_LocalActions extends {
         [actionType: string]: any;
     } = {},
-    SUBDUXES extends Record<string, Dux> = {},
+    T_Subduxes extends Record<string, Dux> = {},
 > {
     #localInitial: T_LocalState;
     #localActions: T_LocalActions;
     #localMutations: Record<
         string,
-        Mutation<ActionCreator<any>, AggregateState<T_LocalState>>
+        Mutation<ActionCreator<any>, AggregateState<T_LocalState, T_Subduxes>>
     > = {};
-    #subduxes: SUBDUXES;
+    #subduxes: T_Subduxes;
 
     #name: string;
 
-    #actions: AggregateActions<ResolveActions<T_LocalActions>, SUBDUXES>;
+    #actions: AggregateActions<ResolveActions<T_LocalActions>, T_Subduxes>;
+
+    #initial: AggregateState<T_LocalState, T_Subduxes>;
 
     constructor(
         config: Partial<{
             initial: T_LocalState;
             actions: T_LocalActions;
-            subduxes: SUBDUXES;
+            subduxes: T_Subduxes;
         }>,
     ) {
         // TODO check that we can't alter the initial after the fact
         this.#localInitial = config.initial ?? ({} as T_LocalState);
         this.#localActions = config.actions ?? ({} as T_LocalActions);
-        this.#subduxes = config.subduxes ?? ({} as SUBDUXES);
+        this.#subduxes = config.subduxes ?? ({} as T_Subduxes);
 
         this.#actions = buildActions(this.#localActions, this.#subduxes);
+
+        this.#initial = buildInitial(this.#localInitial, this.#subduxes);
     }
 
     get actions() {
@@ -94,7 +91,7 @@ export default class Updux<
 
     // TODO memoize?
     get initial() {
-        return this.#localInitial;
+        return this.#initial;
     }
 
     createStore(
@@ -114,7 +111,7 @@ export default class Updux<
     // TODO force the actionCreator to be one of the actions?
     mutation<A extends ActionCreator<any>>(
         actionCreator: A,
-        mutation: Mutation<A, AggregateState<T_LocalState>>,
+        mutation: Mutation<A, AggregateState<T_LocalState, T_Subduxes>>,
     ) {
         this.#localMutations[(actionCreator as any).type] = mutation;
     }
diff --git a/src/buildInitial.test.ts b/src/buildInitial.test.ts
new file mode 100644
index 0000000..63743e8
--- /dev/null
+++ b/src/buildInitial.test.ts
@@ -0,0 +1,21 @@
+import { test, expect } from 'vitest';
+import { buildInitial } from './initial.js';
+
+test('basic', () => {
+    expect(
+        buildInitial(
+            { a: 1 },
+            { b: { initial: { c: 2 } }, d: { initial: 'e' } },
+        ),
+    ).toEqual({
+        a: 1,
+        b: { c: 2 },
+        d: 'e',
+    });
+});
+
+test('throw if subduxes and initial is not an object', () => {
+    expect(() => {
+        buildInitial(3, { bar: 'foo' });
+    }).toThrow();
+});
diff --git a/src/initial.test.todo b/src/initial.test.todo
deleted file mode 100644
index 0aa2a85..0000000
--- a/src/initial.test.todo
+++ /dev/null
@@ -1,46 +0,0 @@
-import { test, expect } from 'vitest';
-
-import { Updux } from './Updux.js';
-
-const bar = new Updux({ initial: 123 });
-
-const foo = new Updux({
-    initial: { root: 'abc' },
-    subduxes: {
-        bar,
-    },
-});
-
-test('single dux', () => {
-    const foo = new Updux({
-        initial: { a: 1 },
-    });
-
-    expect(foo.initial).toEqual({ a: 1 });
-});
-
-test('initial value', () => {
-    expect(foo.initial).toEqual({
-        root: 'abc',
-        bar: 123,
-    });
-});
-
-test('splat initial', async () => {
-    const bar = new Updux({
-        initial: { id: 0 },
-    });
-
-    const foo = new Updux({
-        subduxes: { '*': bar },
-    });
-
-    expect(foo.initial).toEqual([]);
-
-    expect(
-        new Updux({
-            initial: 'overriden',
-            subduxes: { '*': bar },
-        }).initial,
-    ).toEqual('overriden');
-});
diff --git a/src/initial.test.ts b/src/initial.test.ts
index 32194e6..245632a 100644
--- a/src/initial.test.ts
+++ b/src/initial.test.ts
@@ -1,5 +1,15 @@
+import { expectType } from './tutorial.test.js';
 import Updux from './Updux.js';
 
+const bar = new Updux({ initial: 123 });
+
+const foo = new Updux({
+    initial: { root: 'abc' },
+    subduxes: {
+        bar,
+    },
+});
+
 test('default', () => {
     const { initial } = new Updux({});
 
@@ -29,3 +39,60 @@ test('initial to createStore', () => {
         b: 4,
     });
 });
+
+test('single dux', () => {
+    const foo = new Updux({
+        initial: { a: 1 },
+    });
+
+    expect(foo.initial).toEqual({ a: 1 });
+});
+
+// TODO add 'check for no todo eslint rule'
+test('initial value', () => {
+    expect(foo.initial).toEqual({
+        root: 'abc',
+        bar: 123,
+    });
+
+    expectType<{
+        root: string;
+        bar: number;
+    }>(foo.initial);
+});
+
+test('no initial', () => {
+    const dux = new Updux({});
+    expectType<{}>(dux.initial);
+    expect(dux.initial).toEqual({});
+});
+
+test('no initial for subdux', () => {
+    const dux = new Updux({
+        subduxes: {
+            bar: new Updux({}),
+            baz: new Updux({ initial: 'potato' }),
+        },
+    });
+    expectType<{ bar: {}; baz: string }>(dux.initial);
+    expect(dux.initial).toEqual({ bar: {}, baz: 'potato' });
+});
+
+test.todo('splat initial', async () => {
+    const bar = new Updux({
+        initial: { id: 0 },
+    });
+
+    const foo = new Updux({
+        subduxes: { '*': bar },
+    });
+
+    expect(foo.initial).toEqual([]);
+
+    expect(
+        new Updux({
+            initial: 'overriden',
+            subduxes: { '*': bar },
+        }).initial,
+    ).toEqual('overriden');
+});
diff --git a/src/initial.ts b/src/initial.ts
new file mode 100644
index 0000000..36aaf92
--- /dev/null
+++ b/src/initial.ts
@@ -0,0 +1,23 @@
+import u from '@yanick/updeep-remeda';
+import * as R from 'remeda';
+
+type SubduxState<S> = 'initial' extends keyof S ? S['initial'] : {};
+
+export type AggregateState<LOCAL, SUBDUXES extends Record<any, any>> = LOCAL &
+    (keyof SUBDUXES extends never
+        ? {}
+        : {
+              [Slice in keyof SUBDUXES]: Slice extends string
+                  ? SubduxState<SUBDUXES[Slice]>
+                  : never;
+          });
+
+export function buildInitial(localInitial, subduxes) {
+    if (Object.keys(subduxes).length > 0 && typeof localInitial !== 'object') {
+        throw new Error(
+            "can't have subduxes when the initial value is not an object",
+        );
+    }
+
+    return u(localInitial, R.mapValues(subduxes, R.pathOr(['initial'], {})));
+}
diff --git a/src/tutorial.test.ts b/src/tutorial.test.ts
index 753e746..e763eb4 100644
--- a/src/tutorial.test.ts
+++ b/src/tutorial.test.ts
@@ -1,7 +1,7 @@
 import Updux, { createAction, withPayload } from './index.js';
 import u from '@yanick/updeep-remeda';
 
-const expectType = <T>(value: T) => value;
+export const expectType = <T>(value: T) => value;
 
 test('initial state', () => {
     const initial = {