diff --git a/public/include/pages/register/register.inc.php b/public/include/pages/register/register.inc.php
index 3c63963b..95066311 100644
--- a/public/include/pages/register/register.inc.php
+++ b/public/include/pages/register/register.inc.php
@@ -8,8 +8,8 @@ if ($setting->getValue('recaptcha_enabled')) {
   $rsp = recaptcha_check_answer (
     $setting->getValue('recaptcha_private_key'),
     $_SERVER["REMOTE_ADDR"],
-    $_POST["recaptcha_challenge_field"],
-    $_POST["recaptcha_response_field"]
+    ( (isset($_POST["recaptcha_challenge_field"])) ? $_POST["recaptcha_challenge_field"] : null ),
+    ( (isset($_POST["recaptcha_response_field"])) ? $_POST["recaptcha_response_field"] : null )
   );
 }
 
@@ -19,7 +19,7 @@ if ($setting->getValue('disable_invitations') && $setting->getValue('lock_regist
   $_SESSION['POPUP'][] = array('CONTENT' => 'Only invited users are allowed to register.', 'TYPE' => 'errormsg');
 } else {
   // Check if recaptcha is enabled, process form data if valid
-  if($setting->getValue('recaptcha_enabled') && $_POST["recaptcha_response_field"] && $_POST["recaptcha_response_field"]!=''){
+  if($setting->getValue('recaptcha_enabled') && isset($_POST["recaptcha_response_field"]) && $_POST["recaptcha_response_field"]!=''){
     if ($rsp->is_valid) {
       $smarty->assign("RECAPTCHA", recaptcha_get_html($setting->getValue('recaptcha_public_key')));
       isset($_POST['token']) ? $token = $_POST['token'] : $token = '';