diff --git a/typo3/sysext/frontend/Classes/ContentObject/ContentObjectRenderer.php b/typo3/sysext/frontend/Classes/ContentObject/ContentObjectRenderer.php
index 80e462e109de45282ea5a1aa5b9e35c0def933f2..19d60b7060361a5b9bb98363d9a16f415817e6cc 100644
--- a/typo3/sysext/frontend/Classes/ContentObject/ContentObjectRenderer.php
+++ b/typo3/sysext/frontend/Classes/ContentObject/ContentObjectRenderer.php
@@ -4917,7 +4917,7 @@ class ContentObjectRenderer implements LoggerAwareInterface
         }
         if (is_array($urlParameters)) {
             if (!empty($urlParameters)) {
-                $conf['additionalParams'] .= HttpUtility::buildQueryString($urlParameters, '&');
+                $conf['additionalParams'] = ($conf['additionalParams'] ?? '') . HttpUtility::buildQueryString($urlParameters, '&');
             }
         } else {
             $conf['additionalParams'] = ($conf['additionalParams'] ?? '') . $urlParameters;