PHP Fatal error:Cannot use object of type stdClass as array in Cannot use object of type stdClass as array in mailchimp_signup.admin.inc

After upgrading to 7.x-4.0, I'm getting a fatal error when visiting a page with a mailchimp signup block:

PHP Fatal error: Cannot use object of type stdClass as array in .../mailchimp/modules/mailchimp_signup/includes/mailchimp_signup.admin.inc on line 160

Sure enough, you can see in the code that $mergevar is an object, and so it needs the name assigned as an object property and not an array member.

This fixes it:

@@ -157,7 +157,8 @@ function mailchimp_signup_form($form, &$form_state, MailchimpSignup $signup) {
       foreach ($list_mergevars as $mergevar) {
         $form_state['mergevar_options'][$mergevar->tag] = $mergevar;
         if (!$mergevar->public) {
-          $form_state['mergevar_options'][$mergevar->tag]['name'] .= ' (private)';
+          $form_state['mergevar_options'][$mergevar->tag]->name .= ' (private)';
         };
       }
     }