diff --git a/inc/maiken/app.hpp b/inc/maiken/app.hpp
index 4fb1886f..49c45850 100644
--- a/inc/maiken/app.hpp
+++ b/inc/maiken/app.hpp
@@ -35,6 +35,7 @@ namespace maiken {
 class Application;
 }
 
+#include <cstdint>
 #include <optional>
 
 #include "maiken/defs.hpp"