diff --git a/lib/core/index.js b/lib/core/index.js
index 920e55b9..953310a4 100644
--- a/lib/core/index.js
+++ b/lib/core/index.js
@@ -201,7 +201,7 @@ module.exports = function createMiddleware(_dir, _options) {
       )
     );
     // determine compressed forms if they were to exist
-    gzippedFile = `${file}.gz`;
+    gzippedFile = file.slice(-3) === ".gz" ? file : `${file}.gz`;
     brotliFile = `${file}.br`;
 
     Object.keys(headers).forEach((key) => {