diff --git a/packages/backend/src/misc/populate-emojis.ts b/packages/backend/src/misc/populate-emojis.ts
index 26c05e5fa..6681578c9 100644
--- a/packages/backend/src/misc/populate-emojis.ts
+++ b/packages/backend/src/misc/populate-emojis.ts
@@ -63,7 +63,7 @@ export async function populateEmoji(emojiName: string, noteUserHost: string | nu
 
 	const isLocal = emoji.host == null;
 	const emojiUrl = emoji.publicUrl || emoji.originalUrl; // || emoji.originalUrl してるのは後方互換性のため
-	const url = isLocal ? emojiUrl : `${config.url}/proxy/image.png?${query({ url: emojiUrl })}`;
+	const url = isLocal ? emojiUrl : `${config.url}/proxy/image.webp?${query({ url: emojiUrl })}`;
 
 	return {
 		name: emojiName,
diff --git a/packages/backend/src/server/web/url-preview.ts b/packages/backend/src/server/web/url-preview.ts
index 71465c808..1af82954e 100644
--- a/packages/backend/src/server/web/url-preview.ts
+++ b/packages/backend/src/server/web/url-preview.ts
@@ -44,7 +44,7 @@ module.exports = async (ctx: Koa.Context) => {
 function wrap(url?: string): string | null {
 	return url != null
 		? url.match(/^https?:\/\//)
-			? `${config.url}/proxy/preview.jpg?${query({
+			? `${config.url}/proxy/preview.webp?${query({
 				url,
 				preview: '1',
 			})}`