diff --git a/include/boost/ref.hpp b/include/boost/ref.hpp
index a13558b..ff5394c 100644
--- a/include/boost/ref.hpp
+++ b/include/boost/ref.hpp
@@ -5,6 +5,8 @@
 #  pragma once
 # endif
 
+# include <boost/config.hpp>
+
 //
 //  ref.hpp - ref/cref, useful helper functions
 //