diff --git a/Chaos/Md4.hpp b/Chaos/Md4.hpp
index 122eaf4..8cd0337 100644
--- a/Chaos/Md4.hpp
+++ b/Chaos/Md4.hpp
@@ -3,6 +3,7 @@
 
 #include <cstdint>
 #include <array>
+#include <string>
 
 namespace Chaos::Md4
 {