diff --git a/mailpoet/lib/Services/AuthorizedSenderDomainController.php b/mailpoet/lib/Services/AuthorizedSenderDomainController.php
index 9c0eb3f553..4fd73c083b 100644
--- a/mailpoet/lib/Services/AuthorizedSenderDomainController.php
+++ b/mailpoet/lib/Services/AuthorizedSenderDomainController.php
@@ -291,7 +291,7 @@ class AuthorizedSenderDomainController {
     return $this->subscribers->getSubscribersCount() > self::UPPER_LIMIT;
   }
 
-  private function restrictionsApply() {
+  private function restrictionsApply(): bool {
     if ($this->settingsController->get('mta.method') !== Mailer::METHOD_MAILPOET) {
       return false;
     }