diff --git a/utility.hpp b/utility.hpp
index c4ade09..89fcafc 100644
--- a/utility.hpp
+++ b/utility.hpp
@@ -3,6 +3,7 @@
 
 #include "status_code.hpp"
 #include <atomic>
+#include <cstdlib>
 #include <iostream>
 #include <memory>
 #include <string>