diff --git a/packages/backend/src/core/SignupService.ts b/packages/backend/src/core/SignupService.ts
index 2b8387f89..364bcf0f8 100644
--- a/packages/backend/src/core/SignupService.ts
+++ b/packages/backend/src/core/SignupService.ts
@@ -80,14 +80,16 @@ export class SignupService {
 			throw new Error('USED_USERNAME');
 		}
 
-		if (!opts.ignorePreservedUsernames) {
+		const isTheFirstUser = (await this.usersRepository.countBy({ host: IsNull() })) === 0;
+
+		if (!opts.ignorePreservedUsernames || !isTheFirstUser) {
 			const instance = await this.metaService.fetch(true);
 			const isPreserved = instance.preservedUsernames.map(x => x.toLowerCase()).includes(username.toLowerCase());
 			if (isPreserved) {
 				throw new Error('USED_USERNAME');
 			}
 		}
-	
+
 		const keyPair = await new Promise<string[]>((res, rej) =>
 			generateKeyPair('rsa', {
 				modulusLength: 4096,
@@ -123,9 +125,7 @@ export class SignupService {
 				usernameLower: username.toLowerCase(),
 				host: this.utilityService.toPunyNullable(host),
 				token: secret,
-				isRoot: (await this.usersRepository.countBy({
-					host: IsNull(),
-				})) === 0,
+				isRoot: isTheFirstUser,
 			}));
 	
 			await transactionalEntityManager.save(new UserKeypair({
diff --git a/packages/backend/src/server/api/SignupApiService.ts b/packages/backend/src/server/api/SignupApiService.ts
index f3a1d406a..b2bd7d82e 100644
--- a/packages/backend/src/server/api/SignupApiService.ts
+++ b/packages/backend/src/server/api/SignupApiService.ts
@@ -169,7 +169,6 @@ export class SignupApiService {
 			try {
 				const { account, secret } = await this.signupService.signup({
 					username, password, host,
-					ignorePreservedUsernames: (await this.usersRepository.countBy({ host: IsNull() })) === 0,
 				});
 	
 				const res = await this.userEntityService.pack(account, account, {