diff --git a/src/Countdown.jsx b/src/Countdown.jsx
index 4318146..3c8b2fa 100644
--- a/src/Countdown.jsx
+++ b/src/Countdown.jsx
@@ -8,7 +8,7 @@ import style from './Countdown.sass';
 
 export default class Countdown extends React.Component {
   static propTypes = {
-    date: PropTypes.object.isRequired,
+    date: PropTypes.instanceOf(moment).isRequired,
     locale: PropTypes.string,
     minimumIntegerDigits: PropTypes.number,
     useGrouping: PropTypes.bool,