diff --git a/core/lib/Drupal/Component/Utility/Html.php b/core/lib/Drupal/Component/Utility/Html.php
index 5456cfa..5bdb7e4 100644
--- a/core/lib/Drupal/Component/Utility/Html.php
+++ b/core/lib/Drupal/Component/Utility/Html.php
@@ -68,6 +68,7 @@ class Html {
    *   The cleaned class name.
    */
   public static function getClass($class) {
+    $class = (string) $class;
     if (!isset(static::$classes[$class])) {
       static::$classes[$class] = static::cleanCssIdentifier(Unicode::strtolower($class));
     }