diff --git a/assets/php/contact_form.php b/assets/php/contact_form.php
index c2fb857..9b2c73c 100644
--- a/assets/php/contact_form.php
+++ b/assets/php/contact_form.php
@@ -33,7 +33,7 @@ function prepare_message_body(string $message, string $name) {
  *  mail(): Braucht auf dem Server einen korrekt konfigurierten Mailserver
  *  phpmailer: Bibliothek, der per Composer installiert wird. Tut ganz gut mit SMTP.
  */
-function send_message_to_office($subject, $message, $name, $email) {
+function send_message_to_office(string $subject, string $message, string $name, string $email) {
     return mail(
         getenv('WTF_CONTACT_TO'),
         "=?UTF-8?B?" . base64_encode($subject) . "?=",
@@ -48,7 +48,7 @@ function send_message_to_office($subject, $message, $name, $email) {
     );
 }
 
-function send_response($response_data) {
+function send_response(array $response_data) {
     $json = json_encode($response_data);
     if ($json === false) {
         // Avoid echo of empty string (which is invalid JSON), and