diff --git a/src/Prismic/Exception/RequestFailureException.php b/src/Prismic/Exception/RequestFailureException.php
index 6918915c..123dc98a 100755
--- a/src/Prismic/Exception/RequestFailureException.php
+++ b/src/Prismic/Exception/RequestFailureException.php
@@ -10,6 +10,7 @@
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 
+/** @final This class is not designed to be open to extension */
 class RequestFailureException extends RuntimeException
 {