diff --git a/src/observer/object.js b/src/observer/object.js
index 751f1a1cf..17874e9f6 100644
--- a/src/observer/object.js
+++ b/src/observer/object.js
@@ -14,16 +14,12 @@ _.define(
   objProto,
   '$add',
   function $add (key, val) {
+    if (this.hasOwnProperty(key)) return
     var ob = this.__ob__
-    if (!ob) {
+    if (!ob || _.isReserved(key)) {
       this[key] = val
       return
     }
-    if (_.isReserved(key)) {
-      _.warn('Refused to $add reserved key: ' + key)
-      return
-    }
-    if (this.hasOwnProperty(key)) return
     ob.convert(key, val)
     if (ob.vms) {
       var i = ob.vms.length
@@ -50,17 +46,12 @@ _.define(
   objProto,
   '$delete',
   function $delete (key) {
-    var ob = this.__ob__
-    if (!ob) {
-      delete this[key]
-      return
-    }
-    if (_.isReserved(key)) {
-      _.warn('Refused to $add reserved key: ' + key)
-      return
-    }
     if (!this.hasOwnProperty(key)) return
     delete this[key]
+    var ob = this.__ob__
+    if (!ob || _.isReserved(key)) {
+      return
+    }
     if (ob.vms) {
       var i = ob.vms.length
       while (i--) {
diff --git a/test/unit/specs/api/data_spec.js b/test/unit/specs/api/data_spec.js
index 462c805e9..783c4050f 100644
--- a/test/unit/specs/api/data_spec.js
+++ b/test/unit/specs/api/data_spec.js
@@ -65,10 +65,9 @@ describe('Data API', function () {
     expect(vm.c).toBe(1)
     expect(vm._data.c).toBe(1)
     expect(vm._digest).toHaveBeenCalled()
-    // reserved key should warn
+    // reserved key should not be proxied
     vm.$add('_c', 1)
     expect(vm._c).toBeUndefined()
-    expect(_.warn).toHaveBeenCalled()
   })
 
   it('$delete', function () {
@@ -77,10 +76,9 @@ describe('Data API', function () {
     expect(vm.hasOwnProperty('a')).toBe(false)
     expect(vm._data.hasOwnProperty('a')).toBe(false)
     expect(vm._digest).toHaveBeenCalled()
-    // reserved key should warn
+    // reserved key should not be deleted
     vm.$delete('_data')
     expect(vm._data).toBeTruthy()
-    expect(_.warn).toHaveBeenCalled()
   })
 
   it('$watch', function (done) {