diff --git a/include/boost/mpl/has_xxx.hpp b/include/boost/mpl/has_xxx.hpp
index 4ef0196..379bd0c 100644
--- a/include/boost/mpl/has_xxx.hpp
+++ b/include/boost/mpl/has_xxx.hpp
@@ -17,6 +17,7 @@
 // $Revision$
 
 #include <boost/mpl/bool.hpp>
+#include <boost/mpl/aux_/na_spec.hpp>
 #include <boost/mpl/aux_/type_wrapper.hpp>
 #include <boost/mpl/aux_/yes_no.hpp>
 #include <boost/mpl/aux_/config/gcc.hpp>