diff --git a/packages/backend/src/server/api/mastodon/converters/note.ts b/packages/backend/src/server/api/mastodon/converters/note.ts
index fc1cfd4be..bea166dc4 100644
--- a/packages/backend/src/server/api/mastodon/converters/note.ts
+++ b/packages/backend/src/server/api/mastodon/converters/note.ts
@@ -118,6 +118,7 @@ export class NoteConverter {
             in_reply_to_account_id: note.replyUserId,
             reblog: reblog.then(reblog => note.text === null ? reblog : null),
             content: text.then(async text => text !== null ? MfmHelpers.toHtml(mfm.parse(text), JSON.parse(note.mentionedRemoteUsers), note.userHost).then(p => p ?? escapeMFM(text)) : ""),
+            content_type: 'text/x.misskeymarkdown',
             text: text,
             created_at: note.createdAt.toISOString(),
             emojis: noteEmoji,
diff --git a/packages/backend/src/server/api/mastodon/entities/status.ts b/packages/backend/src/server/api/mastodon/entities/status.ts
index 1eba560c0..2df5a6f88 100644
--- a/packages/backend/src/server/api/mastodon/entities/status.ts
+++ b/packages/backend/src/server/api/mastodon/entities/status.ts
@@ -18,6 +18,7 @@ namespace MastodonEntity {
         in_reply_to_account_id: string | null;
         reblog: Status | null;
         content: string | undefined;
+        content_type: string;
         text: string | null | undefined;
         created_at: string;
         emojis: Emoji[];