diff --git a/src/Updux.js b/src/Updux.js
index 5524aaf..0ae1d4b 100644
--- a/src/Updux.js
+++ b/src/Updux.js
@@ -1,6 +1,10 @@
 import R from 'remeda';
 
-import { Action, ActionGenerator } from './actions.js';
+import { action } from './actions.js';
+
+function isActionGen(action) {
+    return typeof action === 'function' && action.type;
+}
 
 export class Updux {
     #localInitial = {};
@@ -14,10 +18,25 @@ export class Updux {
         this.#localInitial = config.initial ?? {};
         this.#subduxes = config.subduxes ?? {};
 
-        this.#actions = R.mergeAll([
-            config.actions ?? {},
-            ...Object.values(this.#subduxes).map(R.prop('actions')),
-        ]);
+        this.#actions = R.mapValues(config.actions ?? {}, (arg, name) =>
+            isActionGen(arg) ? arg : action(name, arg),
+        );
+        Object.entries(this.#subduxes).forEach(([slice, sub]) =>
+            this.#addSubduxActions(slice, sub),
+        );
+    }
+
+    #addSubduxActions(_slice, subdux) {
+        if (!subdux.actions) return;
+        // TODO action 'blah' defined multiple times: <where>
+        Object.entries(subdux.actions).forEach(([action, gen]) => {
+            if (this.#actions[action]) {
+                if (this.#actions[action] === gen) return;
+                throw new Error(`action '${action}' already defined`);
+            }
+
+            this.#actions[action] = gen;
+        });
     }
 
     get actions() {
diff --git a/src/actions.test.js b/src/actions.test.js
index b81d8e1..eb6e22f 100644
--- a/src/actions.test.js
+++ b/src/actions.test.js
@@ -51,3 +51,36 @@ test('subduxes actions', () => {
     expect(foo.actions).toHaveProperty('foo');
     expect(foo.actions).toHaveProperty('bar');
 });
+
+test('throw if double action', () => {
+    expect(
+        () =>
+            new Updux({
+                actions: {
+                    foo: action('foo'),
+                },
+                subduxes: {
+                    beta: {
+                        actions: {
+                            foo: action('foo'),
+                        },
+                    },
+                },
+            }),
+    ).toThrow(/action 'foo' already defined/);
+});
+
+test('action definition shortcut', () => {
+    const foo = new Updux({
+        actions: {
+            foo: null,
+            bar: (x) => ({ x }),
+        },
+    });
+
+    expect(foo.actions.foo('hello')).toEqual({ type: 'foo', payload: 'hello' });
+    expect(foo.actions.bar('hello')).toEqual({
+        type: 'bar',
+        payload: { x: 'hello' },
+    });
+});