diff --git a/lib/axios.js b/lib/axios.js
index 7e63e14..72ebb04 100644
--- a/lib/axios.js
+++ b/lib/axios.js
@@ -6,6 +6,7 @@ var spread = require('./spread');
 var axios = module.exports = function axios(config) {
   config = utils.merge({
     method: 'get',
+    headers: {},
     transformRequest: defaults.transformRequest,
     transformResponse: defaults.transformResponse
   }, config);
diff --git a/lib/defaults.js b/lib/defaults.js
index 3baa22f..88c6b7b 100644
--- a/lib/defaults.js
+++ b/lib/defaults.js
@@ -19,7 +19,7 @@ module.exports = {
     }
     if (utils.isObject(data) && !utils.isFile(data) && !utils.isBlob(data)) {
       // Set application/json if no Content-Type has been specified
-      if (utils.isUndefined(headers['Content-Type'])) {
+      if (!utils.isUndefined(headers) && utils.isUndefined(headers['Content-Type'])) {
         headers['Content-Type'] = 'application/json;charset=utf-8';
       }
       return JSON.stringify(data);
diff --git a/lib/utils.js b/lib/utils.js
index 72d696b..516ff6f 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -56,6 +56,16 @@ function isNumber(val) {
   return typeof val === 'number';
 }
 
+/**
+ * Determine if a value is undefined
+ *
+ * @param {Object} val The value to test
+ * @returns {boolean} True if the value is undefined, otherwise false
+ */
+function isUndefined(val) {
+  return typeof val === 'undefined';
+}
+
 /**
  * Determine if a value is an Object
  *
@@ -182,6 +192,7 @@ module.exports = {
   isString: isString,
   isNumber: isNumber,
   isObject: isObject,
+  isUndefined: isUndefined,
   isDate: isDate,
   isFile: isFile,
   isBlob: isBlob,
diff --git a/test/specs/wrapper.spec.js b/test/specs/wrapper.spec.js
index 452fcf4..7ae2cfa 100644
--- a/test/specs/wrapper.spec.js
+++ b/test/specs/wrapper.spec.js
@@ -30,10 +30,7 @@ describe('wrapper', function () {
     axios({
       method: 'post',
       url: '/foo',
-      data: {
-        firstName: 'foo',
-        lastName: 'bar'
-      }
+      data: 'fizz=buzz'
     });
 
     var request = jasmine.Ajax.requests.mostRecent();
@@ -45,6 +42,20 @@ describe('wrapper', function () {
     }
   });
 
+  it('should use application/json when posting an object', function () {
+    axios({
+      url: '/foo/bar',
+      method: 'post',
+      data: {
+        firstName: 'foo',
+        lastName: 'bar'
+      }
+    });
+
+    var request = jasmine.Ajax.requests.mostRecent();
+    expect(request.requestHeaders['Content-Type']).toEqual('application/json;charset=utf-8');
+  });
+
   it('should support binary data as array buffer', function () {
     var input = new Int8Array(2);
     input[0] = 1;
diff --git a/test/unit/utils/isX.js b/test/unit/utils/isX.js
index 306ce3b..c50f43a 100644
--- a/test/unit/utils/isX.js
+++ b/test/unit/utils/isX.js
@@ -19,6 +19,12 @@ module.exports = {
     test.done();
   },
 
+  testIsUndefined: function (test) {
+    test.equals(utils.isUndefined(), true);
+    test.equals(utils.isUndefined(null), false);
+    test.done();
+  },
+
   testIsObject: function (test) {
     test.equals(utils.isObject({}), true);
     test.equals(utils.isObject(null), false);