diff --git a/common/MD5.hpp b/common/MD5.hpp
index fdc1277..4551f7d 100644
--- a/common/MD5.hpp
+++ b/common/MD5.hpp
@@ -1,6 +1,7 @@
 #ifndef COMMON_MD5_HPP
 #define COMMON_MD5_HPP
 
+#include <cstddef>
 #include <cstdint>
 
 typedef struct {