diff --git a/packages/backend/test-federation/test/utils.ts b/packages/backend/test-federation/test/utils.ts
index b5103e00be..7e24bb7904 100644
--- a/packages/backend/test-federation/test/utils.ts
+++ b/packages/backend/test-federation/test/utils.ts
@@ -190,7 +190,8 @@ export async function uploadFile(
 	path = '../../test/resources/192.jpg',
 ): Promise<Misskey.entities.DriveFile> {
 	const filename = path.split('/').pop() ?? 'untitled';
-	const blob = new Blob([await readFile(join(__dirname, path))]);
+	const buffer = await readFile(join(__dirname, path));
+	const blob = new Blob([new Uint8Array(buffer)]);
 
 	const body = new FormData();
 	body.append('i', user.i);