diff --git a/lib/application.js b/lib/application.js
index e5a6b76..39e8a08 100644
--- a/lib/application.js
+++ b/lib/application.js
@@ -5,6 +5,7 @@
 var debug = require('debug')('koa:application');
 var onFinished = require('finished');
 var Emitter = require('events').EventEmitter;
+var Stream = require('stream');
 var compose = require('koa-compose');
 var context = require('./context');
 var request = require('./request');
@@ -174,7 +175,6 @@ function *respond(next) {
 
   var body = this.body;
   var code = this.status = this.status || 404;
-  var head = 'HEAD' == this.method;
 
   // ignore body
   if (status.empty[code]) {
@@ -183,10 +183,12 @@ function *respond(next) {
     return res.end();
   }
 
-  if (null == body) {
-    // empty body
-    if (head) return res.end();
+  if ('HEAD' == this.method) {
+    if (isJSON(body)) this.length = Buffer.byteLength(JSON.stringify(body));
+    return res.end();
+  }
 
+  if (null == body) {
     // status body
     this.type = 'text';
     body = status[code];
@@ -195,27 +197,29 @@ function *respond(next) {
   }
 
   // Buffer body
-  if (Buffer.isBuffer(body)) {
-    if (head) return res.end();
-    return res.end(body);
-  }
+  if (Buffer.isBuffer(body)) return res.end(body);
 
   // string body
-  if ('string' == typeof body) {
-    if (head) return res.end();
-    return res.end(body);
-  }
+  if ('string' == typeof body) return res.end(body);
 
   // Stream body
-  if ('function' == typeof body.pipe) {
-    if (head) return res.end();
-
-    return body.pipe(res);
-  }
+  if (body instanceof Stream) return body.pipe(res);
 
   // body: json
   body = JSON.stringify(body);
   this.length = Buffer.byteLength(body);
-  if (head) return res.end();
   res.end(body);
 }
+
+/**
+ * Check if `body` should be interpreted as json.
+ *
+ */
+
+function isJSON(body) {
+  if (!body) return false;
+  if ('string' == typeof body) return false;
+  if (body instanceof Stream) return false;
+  if (Buffer.isBuffer(body)) return false;
+  return true;
+}
diff --git a/test/application.js b/test/application.js
index 2acc1d7..962b09f 100644
--- a/test/application.js
+++ b/test/application.js
@@ -156,12 +156,34 @@ describe('app.respond', function(){
       .expect(200)
       .end(function(err, res){
         if (err) return done(err);
+        res.should.have.header('Content-Type', 'text/plain; charset=utf-8');
         res.should.have.header('Content-Length', '5');
         assert(0 == res.text.length);
         done();
       });
     })
 
+    it('should keep the headers', function(done){
+      var app = koa();
+
+      app.use(function *(){
+        this.body = { hello: 'world' };
+      });
+
+      var server = app.listen();
+
+      request(server)
+      .head('/')
+      .expect(200)
+      .end(function(err, res){
+        if (err) return done(err);
+        res.should.have.header('Content-Type', 'application/json');
+        res.should.have.header('Content-Length', '17');
+        assert(0 == res.text.length);
+        done();
+      });
+    })
+
     it('should respond with a 404 if no body was set', function(done){
       var app = koa();