diff --git a/src/store.ts b/src/store.ts
index e2bef7b9..8c1aaffb 100644
--- a/src/store.ts
+++ b/src/store.ts
@@ -4,11 +4,12 @@ import { Component } from "./component";
 //------------------------------------------------------------------------------
 // Store Definition
 //------------------------------------------------------------------------------
+
 interface StoreConfig {
   env?: any;
   state?: any;
   actions?: any;
-  mutations?: any;
+  mutations?: { [name: string]: any };
 }
 
 interface StoreOption {
@@ -70,7 +71,11 @@ export class Store extends EventBus {
 
     this._isMutating = true;
     this.observer.allowMutations = true;
-    this.mutations[type].call(null, this.state, payload);
+    this.mutations[type].call(
+      null,
+      { state: this.state, set: this.observer.set },
+      payload
+    );
     this.observer.allowMutations = false;
 
     if (this.debug) {
@@ -83,7 +88,6 @@ export class Store extends EventBus {
     await Promise.resolve();
     if (this._isMutating) {
       this._isMutating = false;
-      // this.observer.disableMutations();
       if (currentRev !== this.observer.__rev__) {
         this.trigger("update", this.state);
       }
@@ -111,6 +115,7 @@ export function makeObserver(): Observer {
 
   function set(target: any, key: number | string, value: any) {
     if (Array.isArray(target)) {
+      // todo
     } else {
       addProp(target, key as string, value);
     }
@@ -124,6 +129,7 @@ export function makeObserver(): Observer {
     value: any
   ) {
     Object.defineProperty(obj, key, {
+      enumerable: true,
       get() {
         return value;
       },
diff --git a/tests/store.test.ts b/tests/store.test.ts
index efb499f0..a504ebb9 100644
--- a/tests/store.test.ts
+++ b/tests/store.test.ts
@@ -11,7 +11,7 @@ describe("basic use", () => {
   test("commit a mutation", () => {
     const state = { n: 1 };
     const mutations = {
-      inc(state, delta) {
+      inc({ state }, delta) {
         state.n += delta;
       }
     };
@@ -25,7 +25,7 @@ describe("basic use", () => {
   test("dispatch an action", () => {
     const state = { n: 1 };
     const mutations = {
-      inc(state, delta) {
+      inc({ state }, delta) {
         state.n += delta;
       }
     };
@@ -57,7 +57,7 @@ describe("basic use", () => {
   test("can dispatch an action in an action", () => {
     const state = { n: 1 };
     const mutations = {
-      inc(state, delta) {
+      inc({ state }, delta) {
         state.n += delta;
       }
     };
@@ -79,10 +79,10 @@ describe("basic use", () => {
   test("dispatch allow synchronizing between actions", async () => {
     const state = { n: 1 };
     const mutations = {
-      inc(state, delta) {
+      inc({ state }, delta) {
         state.n += delta;
       },
-      setN(state, n) {
+      setN({ state }, n) {
         state.n = n;
       }
     };
@@ -117,6 +117,24 @@ describe("basic use", () => {
 
     store.dispatch("someaction");
   });
+
+  test("set function is given to mutations", async () => {
+    let updateCounter = 0;
+    const state = { bertinchamps: "brune" };
+    const mutations = {
+      addInfo({ state, set }) {
+        set(state, "chouffe", "blonde");
+      }
+    };
+    const store = new Store({ state, mutations, actions: {} });
+    store.on("update", null, () => updateCounter++);
+
+    expect(updateCounter).toBe(0);
+    store.commit("addInfo");
+    await nextMicroTick();
+    expect(updateCounter).toBe(1);
+    expect(store.state).toEqual({ bertinchamps: "brune", chouffe: "blonde" });
+  });
 });
 
 describe("observer", () => {
@@ -269,7 +287,7 @@ describe("advanced state properties", () => {
     expect.assertions(3);
     const state = { a: [1, 2, 3] };
     const mutations = {
-      m(state) {
+      m({ state }) {
         expect(state.a.length).toBe(3);
         const l = state.a.push(53);
         expect(l).toBe(4);
@@ -282,7 +300,7 @@ describe("advanced state properties", () => {
 
   test("can use object assign in store", async () => {
     const mutations = {
-      dosomething(state) {
+      dosomething({ state }) {
         Object.assign(state.westmalle, { a: 3, b: 4 });
       }
     };
@@ -296,7 +314,7 @@ describe("advanced state properties", () => {
 
   test("aku reactive store state 1", async () => {
     const mutations = {
-      inc(state) {
+      inc({ state }) {
         state.counter++;
       }
     };
@@ -313,7 +331,7 @@ describe("updates triggered by the store", () => {
     let updateCounter = 0;
     const state = { n: 1 };
     const mutations = {
-      inc(state, delta) {
+      inc({ state }, delta) {
         state.n += delta;
       }
     };
@@ -332,11 +350,11 @@ describe("updates triggered by the store", () => {
     let updateCounter = 0;
     const state = { n: 1 };
     const mutations = {
-      inc(state, delta) {
+      inc({ state }, delta) {
         state.n += delta;
       },
       noop() {},
-      noop2(state) {
+      noop2({ state }) {
         const val = state.n;
         state.n = val;
       }
@@ -387,7 +405,7 @@ describe("connecting a component to store", () => {
   test("connecting a component works", async () => {
     const state = { todos: [] };
     const mutations = {
-      addTodo(state, msg) {
+      addTodo({ state }, msg) {
         state.todos.push({ msg });
       }
     };
@@ -449,7 +467,7 @@ describe("connecting a component to store", () => {
     const state = { todos: [{ id: 1, text: "jupiler" }] };
     let nextId = 2;
     const mutations = {
-      addTodo(state, text) {
+      addTodo({ state }, text) {
         state.todos.push({ text, id: nextId++ });
       }
     };