diff --git a/include/of_util.h b/include/of_util.h
index 20a542a..e284d84 100644
--- a/include/of_util.h
+++ b/include/of_util.h
@@ -1,3 +1,4 @@
+#pragma once
 #include "of_def.hpp"
 #include <cassert>
 #include <iostream>