diff --git a/src/install.js b/src/install.js
index a93ce41ce..d2c5e84e5 100644
--- a/src/install.js
+++ b/src/install.js
@@ -7,16 +7,16 @@ import { bind, update, unbind } from './directive'
 export let Vue
 
 export function install (_Vue) {
-  Vue = _Vue
-
-  const version = (Vue.version && Number(Vue.version.split('.')[0])) || -1
   /* istanbul ignore if */
-  if (process.env.NODE_ENV !== 'production' && install.installed) {
+  if (process.env.NODE_ENV !== 'production' && install.installed && _Vue === Vue) {
     warn('already installed.')
     return
   }
   install.installed = true
 
+  Vue = _Vue
+
+  const version = (Vue.version && Number(Vue.version.split('.')[0])) || -1
   /* istanbul ignore if */
   if (process.env.NODE_ENV !== 'production' && version < 2) {
     warn(`vue-i18n (${install.version}) need to use Vue 2.0 or later (Vue: ${Vue.version}).`)