diff --git a/docroot/modules/contrib/facets/src/Widget/WidgetPluginBase.php b/docroot/modules/contrib/facets/src/Widget/WidgetPluginBase.php
index e33ed28..72db436 100644
--- a/docroot/modules/contrib/facets/src/Widget/WidgetPluginBase.php
+++ b/docroot/modules/contrib/facets/src/Widget/WidgetPluginBase.php
@@ -164,7 +164,7 @@ protected function buildListItems(ResultInterface $result) {
     }
 
     if ($result->isActive()) {
-      $items['#attributes'] = ['class' => 'is-active'];
+      $items['#attributes'] = ['class' => ['is-active']];
     }
 
     $items['#wrapper_attributes'] = ['class' => $classes];