diff --git a/functions.php b/functions.php
index bd0deff..b880e59 100644
--- a/functions.php
+++ b/functions.php
@@ -79,7 +79,9 @@ public function add_security_headers() {
      * Add headers to REST API responses
      */
     public function add_rest_api_headers($response) {
-        $response->header('X-Robots-Tag', 'noindex, nofollow');
+        if ($response instanceof WP_REST_Response) {
+            $response->header('X-Robots-Tag', 'noindex, nofollow');
+        }
         return $response;
     }