diff --git a/CHANGELOG.md b/CHANGELOG.md
index 22e245929..66fc43872 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@
 
 ### Server
 - Fix: `following/invalidate`でフォロワーを解除しようとしているユーザーの情報を返すように
+- Fix: オブジェクトストレージの設定でPrefixを設定していなかった場合nullまたは空文字になる問題を修正
 
 
 ## 2025.2.0
diff --git a/packages/backend/src/core/DriveService.ts b/packages/backend/src/core/DriveService.ts
index c332e5a0a..1550fe3d3 100644
--- a/packages/backend/src/core/DriveService.ts
+++ b/packages/backend/src/core/DriveService.ts
@@ -173,7 +173,8 @@ export class DriveService {
 				?? `${ this.meta.objectStorageUseSSL ? 'https' : 'http' }://${ this.meta.objectStorageEndpoint }${ this.meta.objectStoragePort ? `:${this.meta.objectStoragePort}` : '' }/${ this.meta.objectStorageBucket }`;
 
 			// for original
-			const key = `${this.meta.objectStoragePrefix}/${randomUUID()}${ext}`;
+			const prefix = this.meta.objectStoragePrefix ? `${this.meta.objectStoragePrefix}/` : '';
+			const key = `${prefix}${randomUUID()}${ext}`;
 			const url = `${ baseUrl }/${ key }`;
 
 			// for alts
@@ -190,7 +191,7 @@ export class DriveService {
 			];
 
 			if (alts.webpublic) {
-				webpublicKey = `${this.meta.objectStoragePrefix}/webpublic-${randomUUID()}.${alts.webpublic.ext}`;
+				webpublicKey = `${prefix}webpublic-${randomUUID()}.${alts.webpublic.ext}`;
 				webpublicUrl = `${ baseUrl }/${ webpublicKey }`;
 
 				this.registerLogger.info(`uploading webpublic: ${webpublicKey}`);
@@ -198,7 +199,7 @@ export class DriveService {
 			}
 
 			if (alts.thumbnail) {
-				thumbnailKey = `${this.meta.objectStoragePrefix}/thumbnail-${randomUUID()}.${alts.thumbnail.ext}`;
+				thumbnailKey = `${prefix}thumbnail-${randomUUID()}.${alts.thumbnail.ext}`;
 				thumbnailUrl = `${ baseUrl }/${ thumbnailKey }`;
 
 				this.registerLogger.info(`uploading thumbnail: ${thumbnailKey}`);