diff --git a/lib/core/index.js b/lib/core/index.js
index 920e55b9..8e062c90 100644
--- a/lib/core/index.js
+++ b/lib/core/index.js
@@ -111,6 +111,7 @@ module.exports = function createMiddleware(_dir, _options) {
   const headers = opts.headers;
   const weakEtags = opts.weakEtags;
   const handleOptionsMethod = opts.handleOptionsMethod;
+  const defaultType = opts.contentType || 'application/octet-stream';
 
   opts.root = dir;
   if (defaultExt && /^\./.test(defaultExt)) {
@@ -185,6 +186,7 @@ module.exports = function createMiddleware(_dir, _options) {
     let file = null;
     let gzippedFile = null;
     let brotliFile = null;
+    let contentType = null;
 
     try {
       decodeURIComponent(req.url); // check validity of url
@@ -201,8 +203,11 @@ module.exports = function createMiddleware(_dir, _options) {
       )
     );
     // determine compressed forms if they were to exist
-    gzippedFile = `${file}.gz`;
-    brotliFile = `${file}.br`;
+    gzippedFile = file.endsWith('.gz') ? file : `${file}.gz`;
+    brotliFile = file.endsWith('.br') ? file : `${file}.br`;
+
+    // Do MIME lookup, fall back to octet-stream
+    contentType = mime.lookup(file, defaultType);
 
     Object.keys(headers).forEach((key) => {
       res.setHeader(key, headers[key]);
@@ -227,10 +232,6 @@ module.exports = function createMiddleware(_dir, _options) {
 
 
     function serve(stat) {
-      // Do a MIME lookup, fall back to octet-stream and handle gzip
-      // and brotli special case.
-      const defaultType = opts.contentType || 'application/octet-stream';
-      let contentType = mime.lookup(file, defaultType);
       const range = (req.headers && req.headers.range);
       const lastModified = (new Date(stat.mtime)).toUTCString();
       const etag = generateEtag(stat, weakEtags);
@@ -252,12 +253,8 @@ module.exports = function createMiddleware(_dir, _options) {
 
       if (file === gzippedFile) { // is .gz picked up
         res.setHeader('Content-Encoding', 'gzip');
-        // strip gz ending and lookup mime type
-        contentType = mime.lookup(path.basename(file, '.gz'), defaultType);
       } else if (file === brotliFile) { // is .br picked up
         res.setHeader('Content-Encoding', 'br');
-        // strip br ending and lookup mime type
-        contentType = mime.lookup(path.basename(file, '.br'), defaultType);
       }
 
       if (typeof cacheControl === 'function') {