diff --git a/src/js/api.php b/src/js/api.php
index c0435b0..3b96f14 100644
--- a/src/js/api.php
+++ b/src/js/api.php
@@ -20,6 +20,8 @@ const http = {
 const API = {
 	mastodon: {
 		registerInstance: function(instance) {
+			if (instance === null)
+				instance = document.getElementById('instanceURL').value;
 			http.get('/api/login/mastodon/get_client.php?instance='+encodeURIComponent(instance), {}, function(data) 
 			{
 				data = JSON.parse(data);