diff --git a/include/sta/Debug.hh b/include/sta/Debug.hh
index 089a0bc9..0f3923ae 100644
--- a/include/sta/Debug.hh
+++ b/include/sta/Debug.hh
@@ -25,6 +25,7 @@
 #pragma once
 
 #include <cstdarg>
+#include <mutex>
 
 #include "Map.hh"
 #include "StringUtil.hh"