diff --git a/uw_fdsu_theme_resp.theme b/uw_fdsu_theme_resp.theme
index d9361ce4733bfd920621b2356d3879a8b4d65e2b..b1f9941f62f5f9c1c9861043da3823b97ec862de 100644
--- a/uw_fdsu_theme_resp.theme
+++ b/uw_fdsu_theme_resp.theme
@@ -244,7 +244,7 @@ function uw_fdsu_theme_resp_preprocess_block(&$variables) {
     // set the class to be used to display the admin label.
     if (!in_array($admin_label, $admin_labels_to_exclude)) {
       $variables['admin_label'] = $admin_label;
-      $variables['attributes']['class'] = 'in-layout-builder';
+      $variables['attributes']['class'][] = 'in-layout-builder';
     }
   }
 }