diff --git a/src/Form/ReCaptchaAdminSettingsForm.php b/src/Form/ReCaptchaAdminSettingsForm.php
index 7fccde5fa975baba5fe5b4ff3396d868e57923a8..2d7483ae18846e879fb6b60c6aa45f0596ec3dfb 100644
--- a/src/Form/ReCaptchaAdminSettingsForm.php
+++ b/src/Form/ReCaptchaAdminSettingsForm.php
@@ -101,6 +101,7 @@ class ReCaptchaAdminSettingsForm extends ConfigFormBase {
       '#maxlength' => 4,
       '#title' => $this->t('Tabindex'),
       '#type' => 'number',
+      '#min' => -1,
     ];
     $form['widget']['recaptcha_noscript'] = [
       '#default_value' => $config->get('widget.noscript'),