diff --git a/include/boost/type_traits/type_traits_test.hpp b/include/boost/type_traits/type_traits_test.hpp
index c1a8ac2..81aa050 100644
--- a/include/boost/type_traits/type_traits_test.hpp
+++ b/include/boost/type_traits/type_traits_test.hpp
@@ -379,6 +379,8 @@ struct test_abc2
    virtual void foo2() = 0;
 };
 
+struct incomplete_type;
+
 
 #endif // BOOST_TYPE_TRAITS_TEST_HPP