diff --git a/api_guard/dist/types/index.d.ts b/api_guard/dist/types/index.d.ts
index 2f610e8800..1feac77042 100644
--- a/api_guard/dist/types/index.d.ts
+++ b/api_guard/dist/types/index.d.ts
@@ -209,7 +209,7 @@ export interface InteropObservable<T> {
 
 export declare function interval(period?: number, scheduler?: SchedulerLike): Observable<number>;
 
-export declare function isObservable<T>(obj: any): obj is Observable<T>;
+export declare function isObservable(obj: any): obj is Observable<unknown>;
 
 export declare function lastValueFrom<T>(source: Observable<T>): Promise<T>;
 
diff --git a/src/internal/util/isObservable.ts b/src/internal/util/isObservable.ts
index 407bd2cad0..8df8f328de 100644
--- a/src/internal/util/isObservable.ts
+++ b/src/internal/util/isObservable.ts
@@ -1,3 +1,4 @@
+/** prettier */
 import { Observable } from '../Observable';
 import { isFunction } from './isFunction';
 
@@ -5,7 +6,7 @@ import { isFunction } from './isFunction';
  * Tests to see if the object is an RxJS {@link Observable}
  * @param obj the object to test
  */
-export function isObservable<T>(obj: any): obj is Observable<T> {
+export function isObservable(obj: any): obj is Observable<unknown> {
   // The !! is to ensure that this publicly exposed function returns
   // `false` if something like `null` or `0` is passed.
   return !!obj && (obj instanceof Observable || (isFunction(obj.lift) && isFunction(obj.subscribe)));