diff --git a/core/lib/Drupal/Core/Render/Element/Radio.php b/core/lib/Drupal/Core/Render/Element/Radio.php
index 7f87b92..4eb34ac 100644
--- a/core/lib/Drupal/Core/Render/Element/Radio.php
+++ b/core/lib/Drupal/Core/Render/Element/Radio.php
@@ -37,6 +37,22 @@ public function getInfo() {
     );
   }
 
+ /**
+  * Helper function to cast bool values to string.
+  *
+  * @param bool $value
+  *   A bool value which would be casted to string.
+  *
+  * @return string
+  *   The casted value of the bool value.
+  */
+  protected static function castValue($value)
+  {
+    if (is_bool($value) || (string) (int) $value === (string) $value) {
+        return (string) (int) $index;
+    }
+  }
+
   /**
    * Prepares a #type 'radio' render element for input.html.twig.
    *