diff --git a/test/modifiers.cpp b/test/modifiers.cpp
index e14143c..f67d5c9 100755
--- a/test/modifiers.cpp
+++ b/test/modifiers.cpp
@@ -1,7 +1,7 @@
 #include "test.hpp"
 #include BOOST_TYPEOF_INCREMENT_REGISTRATION_GROUP()
 
-struct x;
+struct x{};
 BOOST_TYPEOF_REGISTER_TYPE(x)
 
 BOOST_STATIC_ASSERT(boost::type_of::test<x*>::value);