diff --git a/plugins/kolab_2fa/lib/Kolab2FA/Driver/Yubikey.php b/plugins/kolab_2fa/lib/Kolab2FA/Driver/Yubikey.php
--- a/plugins/kolab_2fa/lib/Kolab2FA/Driver/Yubikey.php
+++ b/plugins/kolab_2fa/lib/Kolab2FA/Driver/Yubikey.php
@@ -107,6 +107,10 @@
             // truncate the submitted yubikey code to 12 characters
             $value = substr($value, 0, 12);
         }
+        // invalid or no yubikey token provided
+        elseif ($key == 'yubikeyid') {
+            return false;
+        }
 
         return parent::set($key, $value, $persistent);
     }