diff --git a/src/install.js b/src/install.js
index ee8506aa8..259ee4b22 100644
--- a/src/install.js
+++ b/src/install.js
@@ -20,7 +20,7 @@ export function install (Vue) {
 
   Vue.mixin({
     beforeCreate () {
-      if (isDef(this.$options.router)) {
+      if (this.$options.router) {
         this._routerRoot = this
         this._router = this.$options.router
         this._router.init(this)