diff --git a/include/boost/system/detail/system_category_win32.hpp b/include/boost/system/detail/system_category_win32.hpp
index 323eae7..8a86e81 100644
--- a/include/boost/system/detail/system_category_win32.hpp
+++ b/include/boost/system/detail/system_category_win32.hpp
@@ -170,6 +170,7 @@ inline std::string system_category_message_win32( int ev )
     }
 
     local_free lf_ = { lpMsgBuf };
+    (void)lf_;
 
     UINT_ const code_page = message_cp_win32();