diff --git a/src/common/utils/id-parser.ts b/src/common/utils/id-parser.ts
index eb38f0c..97acebf 100644
--- a/src/common/utils/id-parser.ts
+++ b/src/common/utils/id-parser.ts
@@ -1,17 +1,18 @@
 import { BadRequestException } from '@nestjs/common';
 
 export function parseId(raw: string): bigint {
+  const trimmed = raw.trim();
+  if (trimmed === '') {
+    throw new BadRequestException('Invalid id.');
+  }
+  let id: bigint;
   try {
-    const trimmed = raw.trim();
-    if (trimmed === '') {
-      throw new Error('empty');
-    }
-    const id = BigInt(trimmed);
-    if (id < 0n) {
-      throw new Error('negative');
-    }
-    return id;
+    id = BigInt(trimmed);
   } catch {
     throw new BadRequestException('Invalid id.');
   }
+  if (id < 0n) {
+    throw new BadRequestException('Invalid id.');
+  }
+  return id;
 }
diff --git a/src/features/auth/types/oidc-provider.type.spec.ts b/src/features/auth/types/oidc-provider.type.spec.ts
index 96f69e1..182afe8 100644
--- a/src/features/auth/types/oidc-provider.type.spec.ts
+++ b/src/features/auth/types/oidc-provider.type.spec.ts
@@ -1,3 +1,5 @@
+import { BadRequestException } from '@nestjs/common';
+
 import { parseOidcProvider } from '@/features/auth/types/oidc-provider.type';
 
 describe('parseOidcProvider', () => {
@@ -9,17 +11,20 @@ describe('parseOidcProvider', () => {
     expect(parseOidcProvider('kakao')).toBe('kakao');
   });
 
-  it('지원하지 않는 provider이면 에러를 던진다', () => {
+  it('지원하지 않는 provider이면 BadRequestException을 던진다', () => {
+    expect(() => parseOidcProvider('facebook')).toThrow(BadRequestException);
     expect(() => parseOidcProvider('facebook')).toThrow(
       'Unsupported OIDC provider: facebook',
     );
   });
 
-  it('빈 문자열이면 에러를 던진다', () => {
+  it('빈 문자열이면 BadRequestException을 던진다', () => {
+    expect(() => parseOidcProvider('')).toThrow(BadRequestException);
     expect(() => parseOidcProvider('')).toThrow('Unsupported OIDC provider: ');
   });
 
   it('대소문자를 구분한다', () => {
+    expect(() => parseOidcProvider('Google')).toThrow(BadRequestException);
     expect(() => parseOidcProvider('Google')).toThrow(
       'Unsupported OIDC provider: Google',
     );
diff --git a/src/features/auth/types/oidc-provider.type.ts b/src/features/auth/types/oidc-provider.type.ts
index 39ed64d..3d8a2dd 100644
--- a/src/features/auth/types/oidc-provider.type.ts
+++ b/src/features/auth/types/oidc-provider.type.ts
@@ -1,3 +1,5 @@
+import { BadRequestException } from '@nestjs/common';
+
 /**
  * 지원하는 OIDC Provider 타입
  */
@@ -6,10 +8,14 @@ export type OidcProvider = 'google' | 'kakao';
 /**
  * OIDC Provider 파라미터를 검증하고 타입으로 변환한다.
  *
+ * 호출 컨텍스트: HTTP request path (auth.controller 콜백, oidc-login.service).
+ * 따라서 잘못된 값은 도메인 입력 오류로 분류해 4xx 로 반환한다.
+ *
  * @param raw provider 문자열
  * @returns provider 타입
+ * @throws BadRequestException 지원하지 않는 provider 인 경우
  */
 export function parseOidcProvider(raw: string): OidcProvider {
   if (raw === 'google' || raw === 'kakao') return raw;
-  throw new Error(`Unsupported OIDC provider: ${raw}`);
+  throw new BadRequestException(`Unsupported OIDC provider: ${raw}`);
 }
diff --git a/src/global/auth/parse-account-id.ts b/src/global/auth/parse-account-id.ts
index c14f582..684f765 100644
--- a/src/global/auth/parse-account-id.ts
+++ b/src/global/auth/parse-account-id.ts
@@ -3,20 +3,21 @@ import { BadRequestException } from '@nestjs/common';
 import type { JwtUser } from '@/global/auth/types/jwt-payload.type';
 
 export function parseAccountId(user: JwtUser): bigint {
+  const raw =
+    typeof user.accountId === 'string'
+      ? user.accountId.trim()
+      : String(user.accountId ?? '');
+  if (raw === '') {
+    throw new BadRequestException('Invalid account id.');
+  }
+  let id: bigint;
   try {
-    const raw =
-      typeof user.accountId === 'string'
-        ? user.accountId.trim()
-        : String(user.accountId ?? '');
-    if (raw === '') {
-      throw new Error('empty');
-    }
-    const id = BigInt(raw);
-    if (id < 0n) {
-      throw new Error('negative');
-    }
-    return id;
+    id = BigInt(raw);
   } catch {
     throw new BadRequestException('Invalid account id.');
   }
+  if (id < 0n) {
+    throw new BadRequestException('Invalid account id.');
+  }
+  return id;
 }