diff --git a/doc/doxygen_boost_dummy.h b/doc/doxygen_boost_dummy.h
index 6a409cc..ffcc1b0 100644
--- a/doc/doxygen_boost_dummy.h
+++ b/doc/doxygen_boost_dummy.h
@@ -1 +1,3 @@
 namespace boost { template<class T> class shared_ptr { T *dummy; }; }
+
+namespace Sync { class DiffStateContainer { boost::shared_ptr<DiffState> dummy; }; }