diff --git a/packages/backend/src/server/api/mastodon/entities/status_source.ts b/packages/backend/src/server/api/mastodon/entities/status_source.ts
index c73cdbf51..ec85ec105 100644
--- a/packages/backend/src/server/api/mastodon/entities/status_source.ts
+++ b/packages/backend/src/server/api/mastodon/entities/status_source.ts
@@ -3,5 +3,6 @@ namespace MastodonEntity {
         id: string;
         text: string;
         spoiler_text: string;
+        content_type: string;
     };
 }
diff --git a/packages/backend/src/server/api/mastodon/helpers/note.ts b/packages/backend/src/server/api/mastodon/helpers/note.ts
index 75df26f92..2f7d52c2b 100644
--- a/packages/backend/src/server/api/mastodon/helpers/note.ts
+++ b/packages/backend/src/server/api/mastodon/helpers/note.ts
@@ -220,7 +220,8 @@ export class NoteHelpers {
         return {
             id: note.id,
             text: note.text ?? '',
-            spoiler_text: note.cw ?? ''
+            spoiler_text: note.cw ?? '',
+            content_type: 'text/x.misskeymarkdown'
         }
     }