diff --git a/core/lib/Drupal/Core/Render/Element/Textfield.php b/core/lib/Drupal/Core/Render/Element/Textfield.php
index 75b4c4c..db2b816 100644
--- a/core/lib/Drupal/Core/Render/Element/Textfield.php
+++ b/core/lib/Drupal/Core/Render/Element/Textfield.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Core\Render\Element;
 
+use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\Element;
 
 /**
@@ -44,7 +45,7 @@ public function getInfo() {
   /**
    * {@inheritdoc}
    */
-  public static function valueCallback(&$element, $input, &$form_state) {
+  public static function valueCallback(&$element, $input, FormStateInterface $form_state) {
     if ($input !== FALSE && $input !== NULL) {
       // Equate $input to the form value to ensure it's marked for
       // validation.