diff --git a/modules/mailchimp_signup/src/Form/MailchimpSignupPageForm.php b/modules/mailchimp_signup/src/Form/MailchimpSignupPageForm.php
index f0f1073..401aa98 100644
--- a/modules/mailchimp_signup/src/Form/MailchimpSignupPageForm.php
+++ b/modules/mailchimp_signup/src/Form/MailchimpSignupPageForm.php
@@ -111,6 +111,7 @@ class MailchimpSignupPageForm extends FormBase {
       }
     }

+    $mergevars_wrapper_id = isset($list->id) ? $list->id : '';
     $form['mergevars'] = array(
       '#prefix' => '<div id="mailchimp-newsletter-' . $list->id . '-mergefields" class="mailchimp-newsletter-mergefields">',
       '#suffix' => '</div>',