diff --git a/index.d.ts b/index.d.ts
index 7412fcf..31d98ec 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,5 +1,7 @@
-declare function deepmerge<T>(x: Partial<T>, y: Partial<T>, options?: deepmerge.Options): T;
-declare function deepmerge<T1, T2>(x: Partial<T1>, y: Partial<T2>, options?: deepmerge.Options): T1 & T2;
+type PartialDeep<T> = {[K in keyof T]?: PartialDeep<T[K]>};
+
+declare function deepmerge<T>(x: PartialDeep<T>, y: PartialDeep<T>, options?: deepmerge.Options): T;
+declare function deepmerge<T1, T2>(x: PartialDeep<T1>, y: PartialDeep<T2>, options?: deepmerge.Options): T1 & T2;
 
 declare namespace deepmerge {
 	export interface Options {