diff --git a/src/testing/HotObservable.ts b/src/testing/HotObservable.ts
index 69c4451965..defd518f57 100644
--- a/src/testing/HotObservable.ts
+++ b/src/testing/HotObservable.ts
@@ -24,7 +24,7 @@ export class HotObservable<T> extends Subject<T> implements SubscriptionLoggable
     this.scheduler = scheduler;
   }
 
-  _subscribe(subscriber: Subscriber<any>): Subscription {
+  protected _subscribe(subscriber: Subscriber<any>): Subscription {
     const subject: HotObservable<T> = this;
     const index = subject.logSubscribedFrame();
     subscriber.add(new Subscription(() => {