diff --git a/src/Form/SlackInviteSettingsForm.php b/src/Form/SlackInviteSettingsForm.php
index 9f1f2f1..8b3b0e9 100644
--- a/src/Form/SlackInviteSettingsForm.php
+++ b/src/Form/SlackInviteSettingsForm.php
@@ -87,8 +87,8 @@ class SlackInviteSettingsForm extends ConfigFormBase {
         throw new Exception('Failed request');
       }
       // Ensure the correct scope is set.
-      if (isset($response->headers['x-oauth-scopes'][0])) {
-        $scopes = explode(',', $response->headers['x-oauth-scopes'][0]);
+      if ($response->hasHeader('x-oauth-scopes')) {
+        $scopes = explode(',', $response->getHeader('x-oauth-scopes')[0]);
         if (!in_array('admin', $scopes)) {
           $form_state->setErrorByName('slack_invite_token', $this->t('The supplied token is missing the required scope: admin'));
         }