diff --git a/src/operator/do.ts b/src/operator/do.ts
index ed398997f4..09220a068b 100644
--- a/src/operator/do.ts
+++ b/src/operator/do.ts
@@ -4,7 +4,7 @@ import { PartialObserver } from '../Observer';
 import { tap as higherOrder } from '../operators/tap';
 
 /* tslint:disable:max-line-length */
-export function _do<T>(this: Observable<T>, next: (x: T) => void, error?: (e: any) => void, complete?: () => void): Observable<T>;
+export function _do<T>(this: Observable<T>, next?: (x: T) => void, error?: (e: any) => void, complete?: () => void): Observable<T>;
 export function _do<T>(this: Observable<T>, observer: PartialObserver<T>): Observable<T>;
 /* tslint:enable:max-line-length */
 
@@ -52,7 +52,7 @@ export function _do<T>(this: Observable<T>, observer: PartialObserver<T>): Obser
  * @owner Observable
  */
 export function _do<T>(this: Observable<T>, nextOrObserver?: PartialObserver<T> | ((x: T) => void),
-                       error?: (e: any) => void,
-                       complete?: () => void): Observable<T> {
+  error?: (e: any) => void,
+  complete?: () => void): Observable<T> {
   return higherOrder(<any>nextOrObserver, error, complete)(this) as Observable<T>;
 }
diff --git a/src/operators/tap.ts b/src/operators/tap.ts
index b9e43128c4..999f688351 100644
--- a/src/operators/tap.ts
+++ b/src/operators/tap.ts
@@ -8,7 +8,7 @@ import { noop } from '../util/noop';
 import { isFunction } from '../util/isFunction';
 
 /* tslint:disable:max-line-length */
-export function tap<T>(next: (x: T) => void, error?: (e: any) => void, complete?: () => void): MonoTypeOperatorFunction<T>;
+export function tap<T>(next?: (x: T) => void, error?: (e: any) => void, complete?: () => void): MonoTypeOperatorFunction<T>;
 export function tap<T>(observer: PartialObserver<T>): MonoTypeOperatorFunction<T>;
 /* tslint:enable:max-line-length */