diff --git a/index.js b/index.js
index 88862a4..8466622 100644
--- a/index.js
+++ b/index.js
@@ -62,6 +62,11 @@ function got(url, opts, cb) {
 
 	if (body) {
 		opts.method = opts.method || 'POST';
+
+		if (!opts.headers['content-length'] && !opts.headers['transfer-encoding'] && !isStream.readable(body)) {
+			var length = typeof body === 'string' ? Buffer.byteLength(body) : body.length;
+			opts.headers['content-length'] = length;
+		}
 	}
 
 	opts.method = opts.method || 'GET';
diff --git a/readme.md b/readme.md
index bfb48ab..9085cdc 100644
--- a/readme.md
+++ b/readme.md
@@ -70,6 +70,8 @@ _This option and stream mode are mutually exclusive._
 
 Body, that will be sent with `POST` request. If present in `options` and `options.method` is not set - `options.method` will be set to `POST`.
 
+If `content-length` or `transfer-encoding` is not set in `options.headers` and body is String or Buffer - `content-length` will be set to body length.
+
 ###### encoding
 
 Type: `string`, `null`  
diff --git a/test/test-post.js b/test/test-post.js
index a0b7b62..9dabbbe 100644
--- a/test/test-post.js
+++ b/test/test-post.js
@@ -9,6 +9,10 @@ s.on('/', function (req, res) {
 	req.pipe(res);
 });
 
+s.on('/headers', function (req, res) {
+	res.end(JSON.stringify(req.headers));
+});
+
 s.on('/method', function (req, res) {
 	res.setHeader('method', req.method);
 	res.end();
@@ -89,6 +93,30 @@ test('throws on write to stream with body specified', function (t) {
 	setTimeout(t.end.bind(t), 10);
 });
 
+test('post have content-length header to string', function (t) {
+	t.plan(5);
+
+	got(s.url + '/headers', {body: 'wow', json: true}, function (err, headers) {
+		t.equal(headers['content-length'], '3');
+	});
+
+	got(s.url + '/headers', {body: new Buffer('wow'), json: true}, function (err, headers) {
+		t.equal(headers['content-length'], '3');
+	});
+
+	got(s.url + '/headers', {body: from2Array(['wow']), json: true}, function (err, headers) {
+		t.equal(headers['content-length'], undefined);
+	});
+
+	got(s.url + '/headers', {body: 'wow', json: true, headers: {'content-length': '10'}}, function (err, headers) {
+		t.equal(headers['content-length'], '10');
+	});
+
+	got(s.url + '/headers', {body: '3\r\nwow\r\n0\r\n', json: true, headers: {'transfer-encoding': 'chunked'}}, function (err, headers) {
+		t.equal(headers['content-length'], undefined);
+	});
+});
+
 test('cleanup', function (t) {
 	s.close();
 	t.end();