diff --git a/src/operator/find.ts b/src/operator/find.ts
index 5d475bb6d1..3d99ed59a4 100644
--- a/src/operator/find.ts
+++ b/src/operator/find.ts
@@ -45,6 +45,7 @@ export function find<T>(predicate: (value: T, index: number, source: Observable<
 
 export interface FindSignature<T> {
   (predicate: (value: T, index: number, source: Observable<T>) => boolean, thisArg?: any): Observable<T>;
+  <S extends T>(predicate: (value: T, index: number, source: Observable<T>) => value is S, thisArg?: any): Observable<S>;
 }
 
 export class FindValueOperator<T> implements Operator<T, T> {