diff --git a/api_guard/dist/types/operators/index.d.ts b/api_guard/dist/types/operators/index.d.ts
index 96fb7cc2f8..dfdd8396da 100644
--- a/api_guard/dist/types/operators/index.d.ts
+++ b/api_guard/dist/types/operators/index.d.ts
@@ -88,8 +88,7 @@ export declare function distinctUntilChanged<T, K>(comparator: (previous: K, cur
 export declare function distinctUntilKeyChanged<T>(key: keyof T): MonoTypeOperatorFunction<T>;
 export declare function distinctUntilKeyChanged<T, K extends keyof T>(key: K, compare: (x: T[K], y: T[K]) => boolean): MonoTypeOperatorFunction<T>;
 
-export declare function elementAt<T>(index: number): MonoTypeOperatorFunction<T>;
-export declare function elementAt<T, D>(index: number, defaultValue: D): OperatorFunction<T, T | D>;
+export declare function elementAt<T, D = T>(index: number, defaultValue?: D): OperatorFunction<T, T | D>;
 
 export declare function endWith<T>(scheduler: SchedulerLike): MonoTypeOperatorFunction<T>;
 export declare function endWith<T, A>(v1: A, scheduler: SchedulerLike): OperatorFunction<T, T | A>;
diff --git a/src/internal/operators/elementAt.ts b/src/internal/operators/elementAt.ts
index 5b373f910e..464149ad6a 100644
--- a/src/internal/operators/elementAt.ts
+++ b/src/internal/operators/elementAt.ts
@@ -1,14 +1,11 @@
 import { ArgumentOutOfRangeError } from '../util/ArgumentOutOfRangeError';
 import { Observable } from '../Observable';
-import { MonoTypeOperatorFunction, OperatorFunction } from '../types';
+import { OperatorFunction } from '../types';
 import { filter } from './filter';
 import { throwIfEmpty } from './throwIfEmpty';
 import { defaultIfEmpty } from './defaultIfEmpty';
 import { take } from './take';
 
-export function elementAt<T>(index: number): MonoTypeOperatorFunction<T>;
-export function elementAt<T, D>(index: number, defaultValue: D): OperatorFunction<T, T | D>;
-
 /**
  * Emits the single value at the specified `index` in a sequence of emissions
  * from the source Observable.
@@ -55,7 +52,7 @@ export function elementAt<T, D>(index: number, defaultValue: D): OperatorFunctio
  * @return {Observable} An Observable that emits a single item, if it is found.
  * Otherwise, will emit the default value if given. If not, then emits an error.
  */
-export function elementAt<T, D>(index: number, defaultValue?: D): OperatorFunction<T, T | D> {
+export function elementAt<T, D = T>(index: number, defaultValue?: D): OperatorFunction<T, T | D> {
   if (index < 0) {
     throw new ArgumentOutOfRangeError();
   }