diff --git a/src/core/domain/constants/default-media.constants.ts b/src/core/domain/constants/default-media.constants.ts
new file mode 100644
index 00000000..114a292b
--- /dev/null
+++ b/src/core/domain/constants/default-media.constants.ts
@@ -0,0 +1,33 @@
+/**
+ * Storage key of the shared default avatar object.
+ * Mirrors the `avatarUrl` default in `prisma/models/profile.prisma`.
+ */
+export const DEFAULT_AVATAR_KEY = "avatars/default_profile.png";
+
+/**
+ * Storage key of the shared default banner object.
+ * Mirrors the `bannerUrl` default in `prisma/models/profile.prisma`.
+ */
+export const DEFAULT_BANNER_KEY = "banners/default_banner.jpe";
+
+/**
+ * File name stems of the shared default assets, without directory or extension.
+ *
+ * Matching on the stem keeps the guard correct even when the stored value is a
+ * full CDN URL, carries a cache-busting query string, or uses a different
+ * extension than the one written by the Prisma schema default.
+ */
+const DEFAULT_MEDIA_STEMS = ["default_profile", "default_banner"] as const;
+
+/**
+ * Checks whether a stored media path points at a shared default asset.
+ *
+ * Default assets are shared by every user, so they must never be deleted from
+ * storage when a single user replaces their avatar or banner.
+ *
+ * @param mediaPath - The stored avatar/banner path or URL.
+ * @returns True when the path refers to a shared default asset.
+ */
+export function isDefaultMediaKey(mediaPath: string): boolean {
+    return DEFAULT_MEDIA_STEMS.some((stem) => mediaPath.includes(stem));
+}
diff --git a/src/core/use-cases/profile/update-avatar/update-avatar.usecase.ts b/src/core/use-cases/profile/update-avatar/update-avatar.usecase.ts
index 9117a5ba..b9eabe84 100644
--- a/src/core/use-cases/profile/update-avatar/update-avatar.usecase.ts
+++ b/src/core/use-cases/profile/update-avatar/update-avatar.usecase.ts
@@ -3,8 +3,7 @@ import type { UpdateAvatarUseCaseInput } from "./update-avatar-usecase.input";
 import type { StoragePort } from "@core/ports/services/storage.port";
 import type { LoggerPort } from "@core/ports/services/logger.port";
 import { InvalidFileTypeError } from "@core/errors";
-
-const DEFAULT_AVATAR_KEY = "avatars/default_profile.png";
+import { isDefaultMediaKey } from "@core/domain/constants/default-media.constants";
 
 /**
  * Use case for updating a user's profile avatar.
@@ -64,7 +63,7 @@ export class UpdateAvatarUseCase {
             uploadedFilePath,
         );
 
-        if (oldAvatarUrl && !oldAvatarUrl.includes(DEFAULT_AVATAR_KEY)) {
+        if (oldAvatarUrl && !isDefaultMediaKey(oldAvatarUrl)) {
             try {
                 await this.storageService.delete(oldAvatarUrl);
             } catch (error) {
diff --git a/src/core/use-cases/profile/update-banner/update-banner.usecase.ts b/src/core/use-cases/profile/update-banner/update-banner.usecase.ts
index e908adca..31fbd5f0 100644
--- a/src/core/use-cases/profile/update-banner/update-banner.usecase.ts
+++ b/src/core/use-cases/profile/update-banner/update-banner.usecase.ts
@@ -3,8 +3,7 @@ import type { UpdateBannerUseCaseInput } from "./update-banner-usecase.input";
 import { InvalidFileTypeError } from "@core/errors";
 import type { StoragePort } from "@core/ports/services/storage.port";
 import type { LoggerPort } from "@core/ports/services/logger.port";
-
-const DEFAULT_BANNER_KEY = "banners/default_banner.jpeg";
+import { isDefaultMediaKey } from "@core/domain/constants/default-media.constants";
 
 /**
  * Use case for updating a user's profile banner.
@@ -65,7 +64,7 @@ export class UpdateBannerUseCase {
             uploadedFilePath,
         );
 
-        if (oldBannerUrl && !oldBannerUrl.includes(DEFAULT_BANNER_KEY)) {
+        if (oldBannerUrl && !isDefaultMediaKey(oldBannerUrl)) {
             try {
                 await this.storageService.delete(oldBannerUrl);
             } catch (error) {
diff --git a/tests/unit/core/use-cases/profile/update-avatar.usecase.test.ts b/tests/unit/core/use-cases/profile/update-avatar.usecase.test.ts
index c8277fa8..21de2046 100644
--- a/tests/unit/core/use-cases/profile/update-avatar.usecase.test.ts
+++ b/tests/unit/core/use-cases/profile/update-avatar.usecase.test.ts
@@ -4,8 +4,7 @@ import type { IProfileRepository } from "@core/ports/repositories/profile.reposi
 import type { StoragePort } from "@core/ports/services/storage.port";
 import type { LoggerPort } from "@core/ports/services/logger.port";
 import { InvalidFileTypeError } from "@core/errors";
-
-const DEFAULT_AVATAR_KEY = "avatars/default_profile.png";
+import { DEFAULT_AVATAR_KEY } from "@core/domain/constants/default-media.constants";
 
 describe("UpdateAvatarUseCase", () => {
     let useCase: UpdateAvatarUseCase;
diff --git a/tests/unit/core/use-cases/profile/update-banner.usecase.test.ts b/tests/unit/core/use-cases/profile/update-banner.usecase.test.ts
index aa65d97c..34d4a29b 100644
--- a/tests/unit/core/use-cases/profile/update-banner.usecase.test.ts
+++ b/tests/unit/core/use-cases/profile/update-banner.usecase.test.ts
@@ -4,8 +4,7 @@ import type { IProfileRepository } from "@core/ports/repositories/profile.reposi
 import type { StoragePort } from "@core/ports/services/storage.port";
 import type { LoggerPort } from "@core/ports/services/logger.port";
 import { InvalidFileTypeError } from "@core/errors";
-
-const DEFAULT_BANNER_KEY = "banners/default_banner.jpeg";
+import { DEFAULT_BANNER_KEY } from "@core/domain/constants/default-media.constants";
 
 describe("UpdateBannerUseCase", () => {
     let useCase: UpdateBannerUseCase;
@@ -93,6 +92,26 @@ describe("UpdateBannerUseCase", () => {
         expect(storageService.delete).not.toHaveBeenCalled();
     });
 
+    it("should not call storageService.delete for the schema default banner key", async () => {
+        vi.mocked(profileRepository.findBannerByUserId).mockResolvedValue(
+            DEFAULT_BANNER_KEY,
+        );
+
+        await useCase.execute(baseInput);
+
+        expect(storageService.delete).not.toHaveBeenCalled();
+    });
+
+    it("should not call storageService.delete when the default banner carries a cache-busting query", async () => {
+        vi.mocked(profileRepository.findBannerByUserId).mockResolvedValue(
+            `https://cdn.example.com/${DEFAULT_BANNER_KEY}?v=1`,
+        );
+
+        await useCase.execute(baseInput);
+
+        expect(storageService.delete).not.toHaveBeenCalled();
+    });
+
     it("should delete the old banner when it exists and is not the default", async () => {
         const oldUrl = "banners/user-1-old.jpg";
         vi.mocked(profileRepository.findBannerByUserId).mockResolvedValue(