diff --git a/Classes/Controller/Form.php b/Classes/Controller/Form.php
index dd6be810..d1018504 100644
--- a/Classes/Controller/Form.php
+++ b/Classes/Controller/Form.php
@@ -7,6 +7,7 @@
 use TYPO3\CMS\Core\Database\ConnectionPool;
 use TYPO3\CMS\Core\Page\PageRenderer;
 use TYPO3\CMS\Core\Utility\GeneralUtility;
+use TYPO3\CMS\Core\Utility\PathUtility;
 use Typoheads\Formhandler\AjaxHandler\AbstractAjaxHandler;
 use Typoheads\Formhandler\Debugger\AbstractDebugger;
 use Typoheads\Formhandler\Finisher\AbstractFinisher;
@@ -182,6 +183,7 @@ protected function addCSS(): void {
         $file = strval($fileOptions['file'] ?? '');
         if (strlen(trim($file)) > 0) {
           $file = $this->utilityFuncs->resolveRelPathFromSiteRoot($file);
+          $file = PathUtility::getAbsoluteWebPath($file);
 
           GeneralUtility::makeInstance(PageRenderer::class)->addCssFile(
             $file,