diff --git a/core/themes/claro/claro.theme b/core/themes/claro/claro.theme
index 2f23a5758d..2ddca0bf23 100644
--- a/core/themes/claro/claro.theme
+++ b/core/themes/claro/claro.theme
@@ -203,6 +203,11 @@ function claro_preprocess_admin_block(&$variables) {
 function claro_preprocess_admin_block_content(&$variables) {
   foreach ($variables['content'] as &$item) {
     $link_attributes = $item['url']->getOption('attributes') ?: [];
+    if (isset($link_attributes['class']) && is_string($link_attributes['class'])) {
+      $link_attributes['class'] = [
+        $link_attributes['class'],
+      ];
+    }
     $link_attributes['class'][] = 'admin-item__link';
     $item['url']->setOption('attributes', $link_attributes);
     $item['link'] = Link::fromTextAndUrl($item['title'], $item['url']);