diff --git a/cpp/switchchain.hpp b/cpp/switchchain.hpp
index d574263da0d03e66ee0161ec70794773b19ed8e8..34e511d1c602394689504f56908bb64795eec7a8 100644
--- a/cpp/switchchain.hpp
+++ b/cpp/switchchain.hpp
@@ -1,3 +1,4 @@
+#pragma once
 #include "graph.hpp"
 #include <iostream>
 #include <random>