diff --git a/History.md b/History.md
index 2859c77c74..f51da8dfb3 100644
--- a/History.md
+++ b/History.md
@@ -1,3 +1,8 @@
+unreleased
+==========
+
+  * Fix `TypeError` in `res.send` when given `Buffer` and `ETag` header set
+
 4.16.1 / 2017-09-29
 ===================
 
diff --git a/lib/response.js b/lib/response.js
index 832044be9a..9c1796d37b 100644
--- a/lib/response.js
+++ b/lib/response.js
@@ -178,17 +178,17 @@ res.send = function send(body) {
   // populate Content-Length
   var len
   if (chunk !== undefined) {
-    if (!generateETag && chunk.length < 1000) {
+    if (Buffer.isBuffer(chunk)) {
+      // get length of Buffer
+      len = chunk.length
+    } else if (!generateETag && chunk.length < 1000) {
       // just calculate length when no ETag + small chunk
       len = Buffer.byteLength(chunk, encoding)
-    } else if (!Buffer.isBuffer(chunk)) {
+    } else {
       // convert chunk to Buffer and calculate
       chunk = Buffer.from(chunk, encoding)
       encoding = undefined;
       len = chunk.length
-    } else {
-      // get length of Buffer
-      len = chunk.length
     }
 
     this.set('Content-Length', len);
diff --git a/test/res.send.js b/test/res.send.js
index 7aa8d7d90e..2410554248 100644
--- a/test/res.send.js
+++ b/test/res.send.js
@@ -216,6 +216,19 @@ describe('res', function(){
       .expect('Content-Type', 'text/plain; charset=utf-8')
       .expect(200, 'hey', done);
     })
+
+    it('should not override ETag', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        res.type('text/plain').set('ETag', '"foo"').send(Buffer.from('hey'))
+      })
+
+      request(app)
+      .get('/')
+      .expect('ETag', '"foo"')
+      .expect(200, 'hey', done)
+    })
   })
 
   describe('.send(Object)', function(){