diff --git a/src/ast_handlers.hpp b/src/ast_handlers.hpp
index 667cb83..714657e 100644
--- a/src/ast_handlers.hpp
+++ b/src/ast_handlers.hpp
@@ -420,6 +420,8 @@
 
 struct get_class;
 
+struct copy_class;
+
 struct command_class {
     template <typename Iterator, typename Exception, typename Context>
     x3::error_handler_result on_error(Iterator&, Iterator const&, Exception const& x, Context const& context)