diff --git a/src/Utility/InsertFileWidgetUtility.php b/src/Utility/InsertFileWidgetUtility.php
index dea5c91..b787250 100644
--- a/src/Utility/InsertFileWidgetUtility.php
+++ b/src/Utility/InsertFileWidgetUtility.php
@@ -426,7 +426,7 @@ class InsertFileWidgetUtility {
       'element' => $element,
       'field_type' => $fieldType,
       'file' => $file,
-      'class' => $config->get('css_classes.' - $fieldType),
+      'class' => $config->get('css_classes.' . $fieldType),
       'url' => static::aggregateUrl($file->getFileUri(), $absolute),
     );