diff --git a/packages/misskey-js/src/schemas/announcement.ts b/packages/misskey-js/src/schemas/announcement.ts
index eb8b945b5..63b5dc4c8 100644
--- a/packages/misskey-js/src/schemas/announcement.ts
+++ b/packages/misskey-js/src/schemas/announcement.ts
@@ -11,8 +11,12 @@ export const packedAnnouncementSchema = {
 			format: 'date-time',
 		},
 		updatedAt: {
-			type: 'string',
-			format: 'date-time',
+            oneOf: [{
+                type: 'string',
+                format: 'date-time',
+            }, {
+                type: 'null',
+            }],
 		},
         title: {
             type: 'string',