diff --git a/include/boost/detail/reference_content.hpp b/include/boost/detail/reference_content.hpp
index c5abe91..0619912 100644
--- a/include/boost/detail/reference_content.hpp
+++ b/include/boost/detail/reference_content.hpp
@@ -68,7 +68,7 @@ public: // structors
     {
     }
 
-public: // non-Assignable
+private: // non-Assignable
 
     reference_content& operator=(const reference_content&);