diff --git a/lib/middleware.js b/lib/middleware.js
index 2946535..47e0cfa 100644
--- a/lib/middleware.js
+++ b/lib/middleware.js
@@ -34,9 +34,13 @@ module.exports = function middleware(config) {
         };
 
         res.send = body => {
+            const ctype = res.get('Content-Type');
             if(typeof body === 'string' && !req._esiProcessed) {
                 esi.process(body, req.esiOptions).then(oldSend);
             }
+            else if(body instanceof Buffer && ctype && ctype.match(/(text\/)|(\/xml)/) && !req._esiProcessed) {
+                esi.process(body.toString(), req.esiOptions).then(oldSend);
+            }
             else {
                 oldSend(body);
             }
diff --git a/test/middleware-test.js b/test/middleware-test.js
index 8b70f9e..7b4c73e 100644
--- a/test/middleware-test.js
+++ b/test/middleware-test.js
@@ -82,6 +82,28 @@ describe('A express middleware', () => {
         }).catch(done);
     });
 
+    it.only('should fetch external component with a middleware when send is called (buffer version)', done => {
+        // given
+        server.addListener('request', (req, res) => {
+            res.writeHead(200, {'Content-Type': 'text/html'});
+            res.end('<div>test</div>');
+        });
+        app.use(middleware());
+        app.get('/esi', (req, res) => {
+            res.type('text/html');
+            res.send(Buffer.from('<section></section>'));
+        });
+
+        // when
+        const req = gg.get('http://localhost:' + expressPort + '/esi');
+
+        // then
+        req.then(response => {
+            assert.equal(response.body, '<section><div>test</div></section>');
+            done();
+        }).catch(done);
+    });
+
     it('should respect user defined callback in second parameter', done => {
         // given
         server.addListener('request', (req, res) => {