diff --git a/packages/backend/src/misc/correct-filename.ts b/packages/backend/src/misc/correct-filename.ts
index 34cb458a2..9130af44c 100644
--- a/packages/backend/src/misc/correct-filename.ts
+++ b/packages/backend/src/misc/correct-filename.ts
@@ -43,6 +43,8 @@ export function correctFilename(filename: string, ext: string | null) {
 		// jpeg, tiffを同一視
 		dotExt === '.jpg' && filenameExt === '.jpeg' ||
 		dotExt === '.tif' && filenameExt === '.tiff' ||
+		// dllもexeもportable executableなので判定が正しく行われない
+		dotExt === '.exe' && filenameExt === '.dll' ||
 
 		// 圧縮形式っぽければ下手に拡張子を変えない
 		// https://github.com/misskey-dev/misskey/issues/11482