diff --git a/types/shallowequal/index.d.ts b/types/shallowequal/index.d.ts
index 29ffdab8f6..07d54d2b7f 100644
--- a/types/shallowequal/index.d.ts
+++ b/types/shallowequal/index.d.ts
@@ -3,7 +3,7 @@
 // Definitions by: Sean Kelley <https://github.com/seansfkelley>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
-declare function shallowEqual(objA: any, objB: any, compare?: (objA: any, objB: any, indexOrKey?: number | string) => boolean, compareContext?: any): boolean;
+declare function shallowEqual(objA: any, objB: any, compare?: (objA: any, objB: any, indexOrKey?: number | string) => boolean | undefined, compareContext?: any): boolean;
 
 declare namespace shallowEqual { }