diff --git a/package.json b/package.json
index b759dfd..d325450 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "react-countdown",
-  "version": "2.3.5",
+  "version": "2.3.6",
   "description": "A customizable countdown component for React.",
   "main": "./dist/index.js",
   "module": "./dist/index.es.js",
diff --git a/src/Countdown.tsx b/src/Countdown.tsx
index e00fcd7..2c1b77e 100644
--- a/src/Countdown.tsx
+++ b/src/Countdown.tsx
@@ -13,9 +13,9 @@ import {
 } from './utils';
 
 interface Props<T> {
-  children?: React.ReactNode;
-  key?: React.Key;
-  ref?: React.LegacyRef<T>;
+  children?: React.ReactNode | undefined;
+  key?: React.Key | undefined;
+  ref?: React.LegacyRef<T> | undefined;
 }
 
 export interface CountdownProps