diff --git a/lib/defaults.js b/lib/defaults.js
index 5d8aac7..94e9d44 100644
--- a/lib/defaults.js
+++ b/lib/defaults.js
@@ -20,8 +20,16 @@ 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) && utils.isUndefined(headers['Content-Type'])) {
-        headers['Content-Type'] = 'application/json;charset=utf-8';
+      if (!utils.isUndefined(headers)) {
+        utils.forEach(headers, function (val, key) {
+          if (key.toLowerCase() === 'content-type') {
+            headers['Content-Type'] = val;
+          }
+        });
+
+        if (utils.isUndefined(headers['Content-Type'])) {
+          headers['Content-Type'] = 'application/json;charset=utf-8';
+        }
       }
       return JSON.stringify(data);
     }
diff --git a/test/specs/requests.spec.js b/test/specs/requests.spec.js
index 88bde87..3833b63 100644
--- a/test/specs/requests.spec.js
+++ b/test/specs/requests.spec.js
@@ -56,6 +56,29 @@ describe('requests', function () {
     }, 0);
   });
 
+  it('should allow overriding Content-Type header case-insensitive', function (done) {
+    var request, response;
+    var contentType = 'application/vnd.myapp.type+json';
+
+    axios({
+      url: '/foo',
+      method: 'post',
+      data: { prop: 'value' },
+      headers: {
+        'content-type': contentType
+      }
+    }).then(function (res) {
+      response = res;
+    });
+
+    setTimeout(function () {
+      request = jasmine.Ajax.requests.mostRecent();
+      
+      expect(request.requestHeaders['Content-Type']).toEqual(contentType);
+      done();
+    });
+  });
+
   it('should support binary data as array buffer', function (done) {
     var request;
     var input = new Int8Array(2);