diff --git a/src/backends/github/AuthenticationPage.js b/src/backends/github/AuthenticationPage.js
index 97cec461..f7100604 100644
--- a/src/backends/github/AuthenticationPage.js
+++ b/src/backends/github/AuthenticationPage.js
@@ -14,8 +14,13 @@ export default class AuthenticationPage extends React.Component {
 
   handleLogin(e) {
     e.preventDefault();
+    let auth;
+    if (document.location.host.split(':')[0] === 'localhost') {
+      auth = new Authenticator({ site_id: 'cms.netlify.com' });
+    } else {
+      auth = new Authenticator();
+    }
 
-    const auth = new Authenticator({site_id: 'cms.netlify.com'});
     auth.authenticate({provider: 'github', scope: 'repo'}, (err, data) => {
       if (err) {
         this.setState({loginError: err.toString()});
diff --git a/src/lib/netlify-auth.js b/src/lib/netlify-auth.js
index 54a75283..b22b8c6b 100644
--- a/src/lib/netlify-auth.js
+++ b/src/lib/netlify-auth.js
@@ -29,8 +29,8 @@ const PROVIDERS = {
 };
 
 class Authenticator {
-  constructor(config) {
-    this.site_id = config.site_id;
+  constructor(config = {}) {
+    this.site_id = config.site_id || null;
     this.base_url = config.base_url || NETLIFY_API;
   }