diff --git a/packages/backend/src/server/web/url-preview.ts b/packages/backend/src/server/web/url-preview.ts
index b28e813c6..ba3c8e1b4 100644
--- a/packages/backend/src/server/web/url-preview.ts
+++ b/packages/backend/src/server/web/url-preview.ts
@@ -31,7 +31,7 @@ export const urlPreviewHandler = async (ctx: Koa.Context): Promise<void> => {
 		const summary = meta.summalyProxy ? await getJson(`${meta.summalyProxy}?${query({
 			url,
 			lang: lang ?? 'ja-JP',
-		})}`) : await summaly.default(url, {
+		})}`) as Awaited<ReturnType<typeof summaly.default>> : await summaly.default(url, {
 			followRedirects: false,
 			lang: lang ?? 'ja-JP',
 		});
@@ -53,8 +53,8 @@ export const urlPreviewHandler = async (ctx: Koa.Context): Promise<void> => {
 	}
 };
 
-function wrap(url?: string): string | null {
-	return url != null
+function wrap(url: string|null): string|null {
+	return url !== null
 		? url.match(/^https?:\/\//)
 			? `${config.url}/proxy/preview.webp?${query({
 				url,