diff --git a/lib/adapters/http.js b/lib/adapters/http.js
index 10c1c09..2afa323 100644
--- a/lib/adapters/http.js
+++ b/lib/adapters/http.js
@@ -20,6 +20,11 @@ module.exports = function httpAdapter(resolve, reject, config) {
     config.headers || {}
   );
 
+  // Add Content-Length header if data exists
+  if (data) {
+    headers['Content-Length'] = data.length;
+  }
+
   // Parse url
   var parsed = url.parse(config.url);
   var options = {
diff --git a/lib/defaults.js b/lib/defaults.js
index c1d7a67..f9a9d20 100644
--- a/lib/defaults.js
+++ b/lib/defaults.js
@@ -14,7 +14,7 @@ module.exports = {
     return utils.isObject(data) &&
           !utils.isFile(data) &&
           !utils.isBlob(data) ?
-            JSON.stringify(data) : null;
+            JSON.stringify(data) : data;
   }],
 
   transformResponse: [function (data) {
diff --git a/test/unit/defaults.js b/test/unit/defaults.js
new file mode 100644
index 0000000..017fb6d
--- /dev/null
+++ b/test/unit/defaults.js
@@ -0,0 +1,32 @@
+var defaults = require('../../lib/defaults');
+
+module.exports = {
+  testTransformRequestJson: function (test) {
+    var data = defaults.transformRequest[0]({foo: 'bar'});
+
+    test.equals(data, '{"foo":"bar"}');
+    test.done();
+  },
+
+  testTransformRequestString: function (test) {
+    var data = defaults.transformRequest[0]('foo=bar');
+
+    test.equals(data, 'foo=bar');
+    test.done();
+  },
+
+  testTransformResponseJson: function (test) {
+    var data = defaults.transformResponse[0]('{"foo":"bar"}');
+
+    test.equals(typeof data, 'object');
+    test.equals(data.foo, 'bar');
+    test.done();
+  },
+
+  testTransformResponseString: function (test) {
+    var data = defaults.transformResponse[0]('foo=bar');
+
+    test.equals(data, 'foo=bar');
+    test.done();
+  }
+};
\ No newline at end of file