diff --git a/packages/backend/src/server/ActivityPubServerService.ts b/packages/backend/src/server/ActivityPubServerService.ts
index a5fb5b82e3..6a0e1ede86 100644
--- a/packages/backend/src/server/ActivityPubServerService.ts
+++ b/packages/backend/src/server/ActivityPubServerService.ts
@@ -776,6 +776,8 @@ export class ActivityPubServerService {
 			}
 
 			const acct = Acct.parse(request.params.acct);
+			// normalize acct host
+			if (this.utilityService.isSelfHost(acct.host)) acct.host = null;
 
 			const user = await this.usersRepository.findOneBy({
 				usernameLower: acct.username.toLowerCase(),