diff --git a/backend/src/tags/tags.controller.ts b/backend/src/tags/tags.controller.ts
index d7dd5f70..4098f939 100644
--- a/backend/src/tags/tags.controller.ts
+++ b/backend/src/tags/tags.controller.ts
@@ -136,12 +136,13 @@ export const mergeTags = async (
   const superTagId: number = Number(req?.body?.superTagId);
   const subTagIds: number[] = req?.body?.subTagIds;
   const tagsService = new TagsService();
+  let returnSuperTagId = 0;
 
   if (await tagsService.isValidBookInfoId(bookInfoId) === false) {
     await tagsService.releaseConnection();
     return next(new ErrorResponse(errorCode.INVALID_BOOKINFO_ID, 400));
   }
-  if (superTagId !== null
+  if (superTagId !== 0
       && await tagsService.isValidSuperTagId(superTagId, bookInfoId) === false) {
     await tagsService.releaseConnection();
     return next(new ErrorResponse(errorCode.INVALID_TAG_ID, 400));
@@ -151,13 +152,18 @@ export const mergeTags = async (
     return next(new ErrorResponse(errorCode.INVALID_TAG_ID, 400));
   }
   try {
-    await tagsService.mergeTags(bookInfoId, subTagIds, superTagId, parseInt(tokenId, 10));
+    returnSuperTagId = await tagsService.mergeTags(
+      bookInfoId,
+      subTagIds,
+      superTagId,
+      parseInt(tokenId, 10),
+    );
   } catch (e) {
     return next(new ErrorResponse(errorCode.UPDATE_FAIL_TAGS, 500));
   } finally {
     await tagsService.releaseConnection();
   }
-  return res.status(status.OK).send({ id: superTagId });
+  return res.status(status.OK).send({ id: returnSuperTagId });
 };
 
 export const updateSuperTags = async (
diff --git a/backend/src/tags/tags.service.ts b/backend/src/tags/tags.service.ts
index 7e62b6ac..6ad36027 100644
--- a/backend/src/tags/tags.service.ts
+++ b/backend/src/tags/tags.service.ts
@@ -129,8 +129,8 @@ export class TagsService {
       const superTag = await this.superTagRepository.getSuperTags({ id: superTagId });
       const superLogin: string | null = await this.superTagRepository.getSuperTagLogin(superTagId);
 
-      if (superLogin === null) throw new Error(errorCode.CREATE_FAIL_TAGS);
-
+      if (superLogin === null)
+        throw new Error(errorCode.CREATE_FAIL_TAGS);
       superTagsInsertion = {
         id: superTag[0].id,
         content: superTag[0].content,
@@ -178,14 +178,14 @@ export class TagsService {
   async mergeTags(
     bookInfoId: number,
     subTagIds: number[],
-    rawSuperTagId: number | null,
+    rawSuperTagId: number,
     userId: number,
   ) {
-    let superTagId: number | null = 0;
+    let superTagId: number = 0;
 
     try {
       await this.queryRunner.startTransaction();
-      if (rawSuperTagId === null) {
+      if (rawSuperTagId === 0) {
         const defaultTag = await this.superTagRepository.getDefaultTag(bookInfoId);
         if (defaultTag === null) {
           superTagId = await this.superTagRepository.createSuperTag('default', bookInfoId, userId);
@@ -199,6 +199,7 @@ export class TagsService {
     } finally {
       await this.queryRunner.release();
     }
+    return superTagId;
   }
 
   async isExistingSuperTag(superTagId: number, content: string): Promise<boolean> {