diff --git a/src/internal/Observable.ts b/src/internal/Observable.ts
index 2da026f44d..4e0c25e8e8 100644
--- a/src/internal/Observable.ts
+++ b/src/internal/Observable.ts
@@ -64,7 +64,7 @@ export class Observable<T> implements Subscribable<T> {
     return observable;
   }
 
-  subscribe(observerOrNext?: Partial<Observer<T>> | ((value: T) => void)): Subscription;
+  subscribe(observerOrNext?: Partial<Observer<T>> | ((value: T) => void) | null): Subscription;
   /** @deprecated Instead of passing separate callback arguments, use an observer argument. Signatures taking separate callback arguments will be removed in v8. Details: https://rxjs.dev/deprecations/subscribe-arguments */
   subscribe(next?: ((value: T) => void) | null, error?: ((error: any) => void) | null, complete?: (() => void) | null): Subscription;
   /**