diff --git a/include/x11/connection.hpp b/include/x11/connection.hpp
index 3c970912..71ad3032 100644
--- a/include/x11/connection.hpp
+++ b/include/x11/connection.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <xcb/xcb.h>
+#include <cstdlib>
 #include <xpp/core.hpp>
 #include <xpp/generic/factory.hpp>
 #include <xpp/proto/x.hpp>