diff --git a/rmcp.hpp b/rmcp.hpp
index 04d06d9..b18809a 100644
--- a/rmcp.hpp
+++ b/rmcp.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <array>
+#include <cstddef>
 #include <cstdint>
 
 namespace rmcp