diff --git a/posix/flock.hpp b/posix/flock.hpp
index 4fb6282e..16644e8f 100644
--- a/posix/flock.hpp
+++ b/posix/flock.hpp
@@ -6,6 +6,8 @@
  * Copyright 2021-2022, Danny Robson <danny@nerdcruft.net>
  */
 
+#pragma once
+
 #include "./fd.hpp"