diff --git a/src/openrct2/core/Guard.hpp b/src/openrct2/core/Guard.hpp
index 7d2dc23e9a..01469f0c73 100644
--- a/src/openrct2/core/Guard.hpp
+++ b/src/openrct2/core/Guard.hpp
@@ -17,6 +17,7 @@
 #pragma once
 
 #include <stdarg.h>
+#include <stdbool.h>
 
 #ifdef __cplusplus
 extern "C" {