diff --git a/modules/angular2/src/core/zone/ng_zone.ts b/modules/angular2/src/core/zone/ng_zone.ts
index 1ffc4c88c6..aef2e33ff3 100644
--- a/modules/angular2/src/core/zone/ng_zone.ts
+++ b/modules/angular2/src/core/zone/ng_zone.ts
@@ -93,14 +93,14 @@ export class NgZone {
   _onErrorHandler: (error: any, stack: any) => void;
 
   // Number of microtasks pending from _innerZone (& descendants)
-  _pendingMicrotasks: number;
+  _pendingMicrotasks: number = 0;
   // Whether some code has been executed in the _innerZone (& descendants) in the current turn
-  _hasExecutedCodeInInnerZone: boolean;
+  _hasExecutedCodeInInnerZone: boolean = false;
   // run() call depth in _mountZone. 0 at the end of a macrotask
   // zone.run(() => {         // top-level call
   //   zone.run(() => {});    // nested call -> in-turn
   // });
-  _nestedRun: number;
+  _nestedRun: number = 0;
 
   // TODO(vicb): implement this class properly for node.js environment
   // This disabled flag is only here to please cjs tests
@@ -115,15 +115,6 @@ export class NgZone {
    *               enabled in development mode as they significantly impact perf.
    */
   constructor({enableLongStackTrace}) {
-    this._onTurnStart = null;
-    this._onTurnDone = null;
-    this._onEventDone = null;
-    this._onErrorHandler = null;
-
-    this._pendingMicrotasks = 0;
-    this._hasExecutedCodeInInnerZone = false;
-    this._nestedRun = 0;
-
     if (global.zone) {
       this._disabled = false;
       this._mountZone = global.zone;
@@ -142,7 +133,7 @@ export class NgZone {
    *
    * Setting the hook overrides any previously set hook.
    */
-  overrideOnTurnStart(onTurnStartHook: Function): void {
+  overrideOnTurnStart(onTurnStartHook: () => void): void {
     this._onTurnStart = normalizeBlank(onTurnStartHook);
   }
 
@@ -156,7 +147,7 @@ export class NgZone {
    *
    * Setting the hook overrides any previously set hook.
    */
-  overrideOnTurnDone(onTurnDoneHook: Function): void {
+  overrideOnTurnDone(onTurnDoneHook: () => void): void {
     this._onTurnDone = normalizeBlank(onTurnDoneHook);
   }
 
@@ -171,7 +162,7 @@ export class NgZone {
    *
    * Setting the hook overrides any previously set hook.
    */
-  overrideOnEventDone(onEventDoneFn: Function, opt_waitForAsync: boolean = false): void {
+  overrideOnEventDone(onEventDoneFn: () => void, opt_waitForAsync: boolean = false): void {
     var normalizedOnEventDone = normalizeBlank(onEventDoneFn);
     if (opt_waitForAsync) {
       this._onEventDone = () => {
@@ -242,7 +233,7 @@ export class NgZone {
     var errorHandling;
 
     if (enableLongStackTrace) {
-      errorHandling = StringMapWrapper.merge(<any>Zone.longStackTraceZone,
+      errorHandling = StringMapWrapper.merge(Zone.longStackTraceZone,
                                              {onError: function(e) { ngZone._onError(this, e); }});
     } else {
       errorHandling = {onError: function(e) { ngZone._onError(this, e); }};
diff --git a/modules/angular2/tsd.json b/modules/angular2/tsd.json
index ef113b7939..cb6567ac13 100644
--- a/modules/angular2/tsd.json
+++ b/modules/angular2/tsd.json
@@ -21,7 +21,7 @@
       "commit": "be0b6b394f77a59e192ad7cfec18078706e44db5"
     },
     "zone/zone.d.ts": {
-      "commit": "055b3172e8eb374a75826710c4d08677872620d3"
+      "commit": "31e7317c9a0793857109236ef7c7f223305a8aa9"
     },
     "angular-protractor/angular-protractor.d.ts": {
       "commit": "4207593c012565a7ea800ed861ffbe5011e7a501"