diff --git a/packages/backend/src/server/activitypub.ts b/packages/backend/src/server/activitypub.ts
index c35b65674..133dd3606 100644
--- a/packages/backend/src/server/activitypub.ts
+++ b/packages/backend/src/server/activitypub.ts
@@ -148,7 +148,7 @@ router.get('/users/:user/publickey', async ctx => {
 });
 
 // user
-async function userInfo(ctx: Router.RouterContext, user: User | undefined | null) {
+async function userInfo(ctx: Router.RouterContext, user: User | null) {
 	if (user == null) {
 		ctx.status = 404;
 		return;