diff --git a/README.md b/README.md
index 665e306..456955a 100644
--- a/README.md
+++ b/README.md
@@ -103,6 +103,10 @@ __('{a} {a} {b} {b} {b}', {a: 'foo', b: 'bar'})
 
 Get locale from query / cookie and header.
 
+### `context.setLocale()`
+
+Set locale and cookie.
+
 ### `context.__getLocaleOrigin()`
 
 Where does locale come from, could be `query`, `cookie`, `header` and `default`.
diff --git a/index.js b/index.js
index e07bd33..2614787 100644
--- a/index.js
+++ b/index.js
@@ -194,16 +194,7 @@ module.exports = function (app, options) {
 
     // if header not send, set the locale cookie
     if (writeCookie && cookieLocale !== locale && !this.headerSent) {
-      // locale change, need to set cookie
-      const cookieOptions = {
-        // make sure brower javascript can read the cookie
-        httpOnly: false,
-        maxAge: cookieMaxAge,
-        signed: false,
-        domain: cookieDomain,
-      };
-      this.cookies.set(cookieField, locale, cookieOptions);
-      debugSilly('Saved cookie with locale %s', locale);
+      updateCookie(this, locale);
     }
     debug('Locale: %s from %s', locale, localeOrigin);
     debugSilly('Locale: %s from %s', locale, localeOrigin);
@@ -217,6 +208,25 @@ module.exports = function (app, options) {
     this.__getLocale();
     return this.__localeOrigin;
   };
+
+  app.context.__setLocale = function (locale) {
+    this.__locale = locale;
+    this.__localeOrigin = 'set';
+    updateCookie(this, locale);
+  };
+
+  function updateCookie(ctx, locale) {
+    const cookieOptions = {
+      // make sure brower javascript can read the cookie
+      httpOnly: false,
+      maxAge: cookieMaxAge,
+      signed: false,
+      domain: cookieDomain,
+      overwrite: true,
+    };
+    ctx.cookies.set(cookieField, locale, cookieOptions);
+    debugSilly('Saved cookie with locale %s', locale);
+  }
 };
 
 function isObject(obj) {
diff --git a/test/index.test.js b/test/index.test.js
index 34c65a1..b2a8a4f 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -525,30 +525,40 @@ describe('koa-locales.test.js', function () {
     describe('__getLocale and __getLocaleOrigin', function() {
       it('should __getLocale and __getLocaleOrigin from cookie', function () {
         return request(app.callback())
-          .get('/methods')
+          .get('/origin')
           .set('cookie', 'locale=de')
           .expect(200, { locale: 'de', localeOrigin: 'cookie' });
       });
 
       it('should __getLocale and __getLocaleOrigin from query', function () {
         return request(app.callback())
-          .get('/methods?locale=de')
+          .get('/origin?locale=de')
           .expect(200, { locale: 'de', localeOrigin: 'query' });
       });
 
       it('should __getLocale and __getLocaleOrigin from header', function () {
         return request(app.callback())
-          .get('/methods')
+          .get('/origin')
           .set('Accept-Language', 'zh-cn')
           .expect(200, { locale: 'zh-cn', localeOrigin: 'header' });
       });
 
       it('should __getLocale and __getLocaleOrigin from default', function () {
         return request(app.callback())
-          .get('/methods')
+          .get('/origin')
           .expect(200, { locale: 'en-us', localeOrigin: 'default' });
       });
     });
+
+    describe('__setLocale', function() {
+      it('should set locale and cookie', function () {
+        return request(app.callback())
+          .get('/set')
+          .set('cookie', 'locale=de')
+          .expect(200, { locale: 'zh-hk', localeOrigin: 'set' })
+          .expect('Set-Cookie', /^locale=zh\-hk; path=\/; expires=[^;]+ GMT$/);
+      });
+    });
   });
 });
 
@@ -558,7 +568,7 @@ function createApp(options) {
   const fname = options && options.functionName || '__';
 
   app.use(function* () {
-    if (this.path === '/methods') {
+    if (this.path === '/origin') {
       assert(this.__getLocaleOrigin() === this.__getLocaleOrigin());
       this.body = {
         locale: this.__getLocale(),
@@ -567,6 +577,17 @@ function createApp(options) {
       return;
     }
 
+    if (this.path === '/set') {
+      this.__getLocale();
+      this.__setLocale('zh-tw');
+      this.__setLocale('zh-hk');
+      this.body = {
+        locale: this.__getLocale(),
+        localeOrigin: this.__getLocaleOrigin(),
+      };
+      return;
+    }
+
     if (this.url === '/headerSent') {
       this.body = 'foo';
       const that = this;