diff --git a/src/Observable.ts b/src/Observable.ts
index 8de30e816c..8cceaa04d7 100644
--- a/src/Observable.ts
+++ b/src/Observable.ts
@@ -20,6 +20,7 @@ export type ObservableInput<T> = ObservableOrPromise<T> | ArrayOrIterator<T>;
  * @class Observable<T>
  */
 export class Observable<T> {
+  ' tag_class_Observable': T;
 
   public _isScalar: boolean = false;
 
diff --git a/src/Subject.ts b/src/Subject.ts
index c7ea22f3ad..d647d36837 100644
--- a/src/Subject.ts
+++ b/src/Subject.ts
@@ -10,16 +10,20 @@ import {throwError} from './util/throwError';
 import {ObjectUnsubscribedError} from './util/ObjectUnsubscribedError';
 
 export class Subject<T> extends Observable<T> implements Observer<T>, Subscription {
+  ' tag_class_Subject': T;
 
   static create: Function = <T>(destination: Observer<T>, source: Observable<T>): Subject<T> => {
     return new Subject<T>(destination, source);
   };
 
-  constructor(protected destination?: Observer<T>, protected source?: Observable<T>) {
+  constructor(destination?: Observer<T>, source?: Observable<T>) {
     super();
+    this.destination = destination;
     this.source = source;
   }
 
+  protected destination: Observer<T>;
+  protected source: Observable<T>;
   public observers: Observer<T>[] = [];
   public isUnsubscribed: boolean = false;
 
diff --git a/src/observable/ArrayLikeObservable.ts b/src/observable/ArrayLikeObservable.ts
index 926b849654..55f1c1d7b3 100644
--- a/src/observable/ArrayLikeObservable.ts
+++ b/src/observable/ArrayLikeObservable.ts
@@ -6,6 +6,7 @@ import {Subscriber} from '../Subscriber';
 import {Subscription} from '../Subscription';
 
 export class ArrayLikeObservable<T> extends Observable<T> {
+  ' tag_class_ArrayLikeObservable': T;
 
   private mapFn: (x: T, y: number) => T;
 
diff --git a/src/observable/ArrayObservable.ts b/src/observable/ArrayObservable.ts
index 32248bf8da..87071fe6ef 100644
--- a/src/observable/ArrayObservable.ts
+++ b/src/observable/ArrayObservable.ts
@@ -10,6 +10,7 @@ import {Subscription} from '../Subscription';
  *
  */
 export class ArrayObservable<T> extends Observable<T> {
+  ' tag_class_ArrayLikeObservable': T;
 
   /**
    * @param array
diff --git a/src/observable/BoundCallbackObservable.ts b/src/observable/BoundCallbackObservable.ts
index b5a3d5b4b6..1652dca2d3 100644
--- a/src/observable/BoundCallbackObservable.ts
+++ b/src/observable/BoundCallbackObservable.ts
@@ -10,6 +10,8 @@ import {AsyncSubject} from '../subject/AsyncSubject';
  *
  */
 export class BoundCallbackObservable<T> extends Observable<T> {
+  ' tag_class_BoundCallbackObservable': T;
+
   subject: AsyncSubject<T>;
 
   /* tslint:disable:max-line-length */
diff --git a/src/observable/BoundNodeCallbackObservable.ts b/src/observable/BoundNodeCallbackObservable.ts
index 55b46d4185..14defe87be 100644
--- a/src/observable/BoundNodeCallbackObservable.ts
+++ b/src/observable/BoundNodeCallbackObservable.ts
@@ -10,6 +10,8 @@ import {AsyncSubject} from '../subject/AsyncSubject';
  *
  */
 export class BoundNodeCallbackObservable<T> extends Observable<T> {
+  ' tag_class_BoundNodeCallbackObservable': T;
+
   subject: AsyncSubject<T>;
 
   /* tslint:disable:max-line-length */
diff --git a/src/observable/ConnectableObservable.ts b/src/observable/ConnectableObservable.ts
index b353574fd6..f378850e54 100644
--- a/src/observable/ConnectableObservable.ts
+++ b/src/observable/ConnectableObservable.ts
@@ -4,6 +4,7 @@ import {Subscriber} from '../Subscriber';
 import {Subscription} from '../Subscription';
 
 export class ConnectableObservable<T> extends Observable<T> {
+  ' tag_class_ConnectableObservable': T;
 
   protected subject: Subject<T>;
   protected subscription: Subscription;
diff --git a/src/observable/DeferObservable.ts b/src/observable/DeferObservable.ts
index cebc595499..c7598ae641 100644
--- a/src/observable/DeferObservable.ts
+++ b/src/observable/DeferObservable.ts
@@ -7,6 +7,7 @@ import {errorObject} from '../util/errorObject';
  *
  */
 export class DeferObservable<T> extends Observable<T> {
+  ' tag_class_DeferObservable': T;
 
   /**
    * @param observableFactory
diff --git a/src/observable/EmptyObservable.ts b/src/observable/EmptyObservable.ts
index 160f1f8424..4dc3580af8 100644
--- a/src/observable/EmptyObservable.ts
+++ b/src/observable/EmptyObservable.ts
@@ -7,6 +7,7 @@ import {Subscription} from '../Subscription';
  *
  */
 export class EmptyObservable<T> extends Observable<T> {
+  ' tag_class_EmptyObservable': T;
 
   /**
    * @param scheduler
diff --git a/src/observable/ErrorObservable.ts b/src/observable/ErrorObservable.ts
index 43663fb99b..866b461437 100644
--- a/src/observable/ErrorObservable.ts
+++ b/src/observable/ErrorObservable.ts
@@ -6,6 +6,7 @@ import {Subscription} from '../Subscription';
  *
  */
 export class ErrorObservable extends Observable<any> {
+  ' tag_class_ErrorObservable': any;
 
   /**
    * @param error
diff --git a/src/observable/ForkJoinObservable.ts b/src/observable/ForkJoinObservable.ts
index ce8539a4e8..7fdabdf7e9 100644
--- a/src/observable/ForkJoinObservable.ts
+++ b/src/observable/ForkJoinObservable.ts
@@ -9,6 +9,8 @@ import {isArray} from '../util/isArray';
  *
  */
 export class ForkJoinObservable<T> extends Observable<T> {
+  ' tag_class_ForkJoinObservable': T;
+
   constructor(private sources: Array<Observable<any> | Promise<any>>,
               private resultSelector?: (...values: Array<any>) => T) {
     super();
diff --git a/src/observable/FromEventObservable.ts b/src/observable/FromEventObservable.ts
index 50d8175c92..2d01a35f17 100644
--- a/src/observable/FromEventObservable.ts
+++ b/src/observable/FromEventObservable.ts
@@ -38,6 +38,7 @@ export type EventTargetLike = EventTarget | NodeStyleEventEmmitter | JQueryStyle
  *
  */
 export class FromEventObservable<T, R> extends Observable<T> {
+  ' tag_class_FromEventObservable': [T, R];
 
   /**
    * @param sourceObj
diff --git a/src/observable/FromEventPatternObservable.ts b/src/observable/FromEventPatternObservable.ts
index 20f70d8bea..9e6ef70852 100644
--- a/src/observable/FromEventPatternObservable.ts
+++ b/src/observable/FromEventPatternObservable.ts
@@ -8,6 +8,7 @@ import {Subscriber} from '../Subscriber';
  *
  */
 export class FromEventPatternObservable<T, R> extends Observable<T> {
+  ' tag_class_FromEventPatternObservable': [T, R];
 
   /**
    * @param addHandler
diff --git a/src/observable/FromObservable.ts b/src/observable/FromObservable.ts
index 945fee1467..31c599c5b7 100644
--- a/src/observable/FromObservable.ts
+++ b/src/observable/FromObservable.ts
@@ -19,6 +19,8 @@ const isArrayLike = (<T>(x: any): x is ArrayLike<T> => x && typeof x.length ===
  *
  */
 export class FromObservable<T> extends Observable<T> {
+  ' tag_class_FromObservable': T;
+
   constructor(private ish: ObservableInput<T>, private scheduler: Scheduler) {
     super(null);
   }
diff --git a/src/observable/IfObservable.ts b/src/observable/IfObservable.ts
index c12ba85be1..3b92bffd84 100644
--- a/src/observable/IfObservable.ts
+++ b/src/observable/IfObservable.ts
@@ -3,6 +3,7 @@ import {Subscriber} from '../Subscriber';
 import {Subscription} from '../Subscription';
 
 export class IfObservable<T, R> extends Observable<T> {
+  ' tag_class_IfObservable': [T, R];
 
   static create<T, R>(condition: () => boolean,
                       thenSource?: Observable<T>,
diff --git a/src/observable/IntervalObservable.ts b/src/observable/IntervalObservable.ts
index cf3cdda5d6..a94d4de62d 100644
--- a/src/observable/IntervalObservable.ts
+++ b/src/observable/IntervalObservable.ts
@@ -8,6 +8,8 @@ import {async} from '../scheduler/async';
  *
  */
 export class IntervalObservable extends Observable<number> {
+  ' tag_class_IntervalObservable': any;
+
   /**
    * @param period
    * @param scheduler
diff --git a/src/observable/IteratorObservable.ts b/src/observable/IteratorObservable.ts
index e9390d9c8c..02b611a154 100644
--- a/src/observable/IteratorObservable.ts
+++ b/src/observable/IteratorObservable.ts
@@ -10,6 +10,8 @@ import {Subscription} from '../Subscription';
 import {Subscriber} from '../Subscriber';
 
 export class IteratorObservable<T> extends Observable<T> {
+  ' tag_class_IteratorObservable': T;
+
   private iterator: any;
 
   static create<T>(iterator: any,
diff --git a/src/observable/NeverObservable.ts b/src/observable/NeverObservable.ts
index 373f6749b8..f6a0e68360 100644
--- a/src/observable/NeverObservable.ts
+++ b/src/observable/NeverObservable.ts
@@ -6,6 +6,8 @@ import {noop} from '../util/noop';
  *
  */
 export class NeverObservable<T> extends Observable<T> {
+  ' tag_class_NeverObservable': T;
+
   /**
    * @return {NeverObservable<T>}
    * @static true
diff --git a/src/observable/PromiseObservable.ts b/src/observable/PromiseObservable.ts
index d7a6ed4c0a..8651e66349 100644
--- a/src/observable/PromiseObservable.ts
+++ b/src/observable/PromiseObservable.ts
@@ -8,6 +8,7 @@ import {Subscription} from '../Subscription';
  *
  */
 export class PromiseObservable<T> extends Observable<T> {
+  ' tag_class_PromiseObservable': T;
 
   public value: T;
 
diff --git a/src/observable/RangeObservable.ts b/src/observable/RangeObservable.ts
index 05919fa23e..a4554feaba 100644
--- a/src/observable/RangeObservable.ts
+++ b/src/observable/RangeObservable.ts
@@ -7,6 +7,7 @@ import {Subscriber} from '../Subscriber';
  *
  */
 export class RangeObservable extends Observable<number> {
+  ' tag_class_RangeObservable': any;
 
   /**
    * @param start
diff --git a/src/observable/ScalarObservable.ts b/src/observable/ScalarObservable.ts
index e7b5c6801f..15ad40c67d 100644
--- a/src/observable/ScalarObservable.ts
+++ b/src/observable/ScalarObservable.ts
@@ -4,6 +4,8 @@ import {Subscriber} from '../Subscriber';
 import {Subscription} from '../Subscription';
 
 export class ScalarObservable<T> extends Observable<T> {
+  ' tag_class_ScalarObservable': T;
+
   static create<T>(value: T, scheduler?: Scheduler): ScalarObservable<T> {
     return new ScalarObservable(value, scheduler);
   }
diff --git a/src/observable/SubscribeOnObservable.ts b/src/observable/SubscribeOnObservable.ts
index 3919f1a646..ce4c5d8ca7 100644
--- a/src/observable/SubscribeOnObservable.ts
+++ b/src/observable/SubscribeOnObservable.ts
@@ -6,6 +6,8 @@ import {asap} from '../scheduler/asap';
 import {isNumeric} from '../util/isNumeric';
 
 export class SubscribeOnObservable<T> extends Observable<T> {
+  ' tag_class_SubscribeOnObservable': T;
+
   static create<T>(source: Observable<T>, delay: number = 0, scheduler: Scheduler = asap): Observable<T> {
     return new SubscribeOnObservable(source, delay, scheduler);
   }
diff --git a/src/observable/TimerObservable.ts b/src/observable/TimerObservable.ts
index 3db92b49c5..ad725b2fac 100644
--- a/src/observable/TimerObservable.ts
+++ b/src/observable/TimerObservable.ts
@@ -11,6 +11,7 @@ import {Subscriber} from '../Subscriber';
  *
  */
 export class TimerObservable extends Observable<number> {
+  ' tag_class_TimerObservable': any;
 
   /**
    * @param dueTime
diff --git a/src/observable/UsingObservable.ts b/src/observable/UsingObservable.ts
index a7b2ca941d..cd1107ae71 100644
--- a/src/observable/UsingObservable.ts
+++ b/src/observable/UsingObservable.ts
@@ -3,6 +3,7 @@ import {Subscriber} from '../Subscriber';
 import {Subscription} from '../Subscription';
 
 export class UsingObservable<T> extends Observable<T> {
+  ' tag_class_UsingObservable': T;
 
   static create<T>(resourceFactory: () => Subscription,
                    observableFactory: (resource: Subscription) => Observable<T>): Observable<T> {
diff --git a/src/subject/AsyncSubject.ts b/src/subject/AsyncSubject.ts
index 3a8bb4f487..9f47f83a76 100644
--- a/src/subject/AsyncSubject.ts
+++ b/src/subject/AsyncSubject.ts
@@ -3,6 +3,8 @@ import {Subscriber} from '../Subscriber';
 import {Subscription} from '../Subscription';
 
 export class AsyncSubject<T> extends Subject<T> {
+  ' tag_class_AsyncSubject': T;
+
   value: T = null;
   hasNext: boolean = false;
 
diff --git a/src/subject/BehaviorSubject.ts b/src/subject/BehaviorSubject.ts
index f39367e5c1..1b0b0015a4 100644
--- a/src/subject/BehaviorSubject.ts
+++ b/src/subject/BehaviorSubject.ts
@@ -5,6 +5,7 @@ import {throwError} from '../util/throwError';
 import {ObjectUnsubscribedError} from '../util/ObjectUnsubscribedError';
 
 export class BehaviorSubject<T> extends Subject<T> {
+  ' tag_class_BehaviorSubject': T;
 
   constructor(private _value: T) {
     super();
diff --git a/src/subject/ReplaySubject.ts b/src/subject/ReplaySubject.ts
index f50cda0ff6..ce9837b78b 100644
--- a/src/subject/ReplaySubject.ts
+++ b/src/subject/ReplaySubject.ts
@@ -6,6 +6,8 @@ import {Subscription} from '../Subscription';
 import {ObserveOnSubscriber} from '../operator/observeOn';
 
 export class ReplaySubject<T> extends Subject<T> {
+  ' tag_class_ReplaySubject': T;
+
   private events: ReplayEvent<T>[] = [];
   private scheduler: Scheduler;
   private bufferSize: number;