diff --git a/op/op.Settings.php b/op/op.Settings.php
index 34387ddf3..007620307 100644
--- a/op/op.Settings.php
+++ b/op/op.Settings.php
@@ -152,7 +152,7 @@ if ($action == "saveSettings")
   $settings->_loginFailure = intval($_POST["loginFailure"]);
   $settings->_autoLoginUser = intval($_POST["autoLoginUser"]);
   $settings->_quota = intval($_POST["quota"]);
-  $settings->_undelUserIds = is_array($_POST["undelUserIds"]) ? implode(',', $_POST["undelUserIds"]) : strval($_POST["undelUserIds"]);
+  $settings->_undelUserIds = !empty($_POST["undelUserIds"]) ? (is_array($_POST["undelUserIds"]) ? implode(',', $_POST["undelUserIds"]) : strval($_POST["undelUserIds"])) : '';
   $settings->_encryptionKey = strval($_POST["encryptionKey"]);
   $settings->_cookieLifetime = intval($_POST["cookieLifetime"]);
   $settings->_defaultAccessDocs = intval($_POST["defaultAccessDocs"]);