diff --git a/src/Form/GoogleAnalyticsAdminSettingsForm.php b/src/Form/GoogleAnalyticsAdminSettingsForm.php
index e04e892..9ff1a61 100644
--- a/src/Form/GoogleAnalyticsAdminSettingsForm.php
+++ b/src/Form/GoogleAnalyticsAdminSettingsForm.php
@@ -8,6 +8,7 @@ namespace Drupal\google_analytics\Form;
 
 use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Form\ConfigFormBase;
+use Drupal\Core\Form\FormStateInterface;
 
 /**
  * Configure Google_Analytics settings for this site.
@@ -22,9 +23,9 @@ class GoogleAnalyticsAdminSettingsForm extends ConfigFormBase {
   }
 
   /**
-   * Implements \Drupal\Core\Form\FormInterface::buildForm().
+   * {@inheritdoc}
    */
-  public function buildForm(array $form, array &$form_state) {
+  public function buildForm(array $form, FormStateInterface $form_state) {
     $config = $this->config('google_analytics.settings');
 
     $form['general'] = array(
@@ -495,9 +496,9 @@ class GoogleAnalyticsAdminSettingsForm extends ConfigFormBase {
   }
 
   /**
-   * Implements \Drupal\Core\Form\FormInterface::validateForm().
+   * {@inheritdoc}
    */
-  public function validateForm(array &$form, array &$form_state) {
+  public function validateForm(array &$form, FormStateInterface $form_state) {
     parent::validateForm($form, $form_state);
 
     // Trim custom dimensions and metrics.
@@ -564,9 +565,9 @@ class GoogleAnalyticsAdminSettingsForm extends ConfigFormBase {
   }
 
   /**
-   * Implements \Drupal\Core\Form\FormInterface::submitForm().
+   * {@inheritdoc}
    */
-  public function submitForm(array &$form, array &$form_state) {
+  public function submitForm(array &$form, FormStateInterface $form_state) {
     $config = $this->config('google_analytics.settings');
     $config
       ->set('account', $form_state['values']['google_analytics_account'])