diff --git a/src/core/observer/array.js b/src/core/observer/array.js
index 684e37ece58..2f0f712097b 100644
--- a/src/core/observer/array.js
+++ b/src/core/observer/array.js
@@ -8,7 +8,7 @@ import { def } from '../util/index'
 const arrayProto = Array.prototype
 export const arrayMethods = Object.create(arrayProto)
 
-const methodsToPatch = [
+export const methodsToPatch = [
   'push',
   'pop',
   'shift',
diff --git a/src/core/observer/index.js b/src/core/observer/index.js
index 4a030ed7f99..3a635d68073 100644
--- a/src/core/observer/index.js
+++ b/src/core/observer/index.js
@@ -2,7 +2,7 @@
 
 import Dep from './dep'
 import VNode from '../vdom/vnode'
-import { arrayMethods } from './array'
+import { arrayMethods, methodsToPatch } from './array'
 import {
   def,
   warn,
@@ -16,8 +16,6 @@ import {
   isServerRendering
 } from '../util/index'
 
-const arrayKeys = Object.getOwnPropertyNames(arrayMethods)
-
 /**
  * In some cases we may want to disable observation inside a component's
  * update computation.
@@ -48,7 +46,12 @@ export class Observer {
       const augment = hasProto
         ? protoAugment
         : copyAugment
-      augment(value, arrayMethods, arrayKeys)
+
+      const methods = Object.create(value.constructor.prototype)
+      methodsToPatch.forEach((m) => {
+        if (methods[m]) methods[m] = arrayMethods[m]
+      })
+      augment(value, methods, Object.getOwnPropertyNames(methods))
       this.observeArray(value)
     } else {
       this.walk(value)