diff --git a/packages/client/src/components/notification.vue b/packages/client/src/components/notification.vue
index bf37442b8..38db93da6 100644
--- a/packages/client/src/components/notification.vue
+++ b/packages/client/src/components/notification.vue
@@ -173,6 +173,7 @@ export default defineComponent({
 
 			os.api('users/show', {userId: renoteNotification.user.id}).then((user: misskey.entities.UserDetailed) => {
 				if (user.host != null && user.followersCount === 0) { // リモートユーザーかつローカルの人間が誰もフォローしていない（最新の投稿が取得できない）ユーザー
+					if (user.url === null) { throw new Error('User page URL is Null') };
 					window.open(user.url, '_blank', 'rel="nofollow noopener"');
 				} else {
 					os.pageWindow(notePage(renoteNotification.note));