diff --git a/CHANGELOG.md b/CHANGELOG.md
index 759f2bfc..68a4e142 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 (unreleased)
 ------------------
 * センシティブフラグの判定を `<meta property="rating">` および `rating` ヘッダでも行うように
+* 内蔵サーバー：レスポンスに`Cache-Control`ヘッダを含むように
 * Bluesky（bsky.app）のプレビューに対応
 * `fediverse:creator` のパースに対応
 * 依存関係の更新
diff --git a/src/index.ts b/src/index.ts
index a8f544fd..3e16b633 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -152,6 +152,8 @@ export default function (fastify: FastifyInstance, options: SummalyOptions, done
 			});
 		}
 
+		reply.header('Cache-Control', 'public, max-age=86400, stale-while-revalidate=43200, immutable');
+
 		try {
 			const summary = await summaly(url, {
 				lang: req.query.lang as string,