diff --git a/type-definitions/most.d.ts b/type-definitions/most.d.ts
index 06b159e2..0508360a 100644
--- a/type-definitions/most.d.ts
+++ b/type-definitions/most.d.ts
@@ -1,12 +1,13 @@
-declare type SeedValue<S, V> = { seed: S, value: V };
-declare type TimeValue<V>    = { time: number, value: V };
+declare type SeedValue<S, V>   = { seed: S, value: V };
+declare type UnfoldValue<S, V> = SeedValue<S,V> | { done: true, value?: V }
+declare type TimeValue<V>      = { time: number, value: V };
 
 declare interface Generator<A, B, C> {}
 declare interface Iterable<A> { [Symbol.iterator](): IterableIterator<A> }
 
 declare type CreateGenerator<A> = (...args: Array<any>) => Generator<A|Promise<A>, any, any>;
 
-export interface Sink<A> {
+export interface Sink<A> { 
   event(time: number, value: A): void;
   // end value parameter is deprecated
   end(time: number, value?: A): void;
@@ -228,7 +229,7 @@ export function periodic<A>(period: number, a?: A): Stream<A>;
 export function fromEvent<T extends Event>(event: string, target: any, useCapture?: boolean): Stream<T>;
 export function fromEvent<T>(event: string, target: any): Stream<T>;
 
-export function unfold<A, B, S>(f: (seed: S) => SeedValue<S, B|Promise<B>>, seed: S): Stream<B>;
+export function unfold<A, S>(f: (seed: S) => UnfoldValue<S, A> | Promise<UnfoldValue<S, A>>, seed: S): Stream<A>;
 export function iterate<A>(f: (a: A) => A|Promise<A>, a: A): Stream<A>;
 export function generate<A>(g: CreateGenerator<A>, ...args: Array<any>): Stream<A>;