diff --git a/include/boost/fusion/support/tag_of.hpp b/include/boost/fusion/support/tag_of.hpp
index c7cfbb76..a1ccf12d 100644
--- a/include/boost/fusion/support/tag_of.hpp
+++ b/include/boost/fusion/support/tag_of.hpp
@@ -13,6 +13,7 @@
 #include <boost/mpl/has_xxx.hpp>
 #include <boost/utility/enable_if.hpp>
 #include <boost/mpl/identity.hpp>
+#include <boost/mpl/assert.hpp>
 #include <boost/mpl/bool.hpp>
 #include <boost/mpl/if.hpp>
 #include <utility>
@@ -45,6 +46,39 @@ namespace boost { namespace fusion
     namespace detail
     {
         BOOST_MPL_HAS_XXX_TRAIT_DEF(fusion_tag)
+
+        template<typename Sequence>
+        struct is_specialized
+          : mpl::false_
+        {};
+
+        template <
+            class T0, class T1, class T2, class T3, class T4, 
+            class T5, class T6, class T7, class T8, class T9
+        >
+        struct is_specialized<tuples::tuple<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9> >
+          : mpl::true_
+        {};
+
+        template <class Head, class Tail>
+        struct is_specialized<tuples::cons<Head, Tail> >
+          : mpl::true_
+        {};
+
+        template <>
+        struct is_specialized<tuples::null_type>
+          : mpl::true_
+        {};
+
+        template <typename T, std::size_t N>
+        struct is_specialized<boost::array<T, N> >
+          : mpl::true_
+        {};
+
+        template<typename T1, typename T2>
+        struct is_specialized<std::pair<T1, T2> >
+          : mpl::true_
+        {};
     }
 
     namespace traits
@@ -54,31 +88,15 @@ namespace boost { namespace fusion
           : mpl::if_< detail::is_mpl_sequence<Sequence>,
               mpl::identity<mpl_sequence_tag>,
               mpl::identity<non_fusion_tag> >::type
-        { };
+        {
+            BOOST_MPL_ASSERT_NOT((detail::is_specialized<Sequence>));
+        };
 
         template <typename Sequence>
         struct tag_of<Sequence, typename boost::enable_if<detail::has_fusion_tag<Sequence> >::type>
         {
             typedef typename Sequence::fusion_tag type;
         };
-
-        template <
-            class T0, class T1, class T2, class T3, class T4, 
-            class T5, class T6, class T7, class T8, class T9
-        >
-        struct tag_of<tuples::tuple<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9> >;
-
-        template <class Head, class Tail>
-        struct tag_of<tuples::cons<Head, Tail> >;
-
-        template <>
-        struct tag_of<tuples::null_type>;
-
-        template <typename T, std::size_t N>
-        struct tag_of<boost::array<T, N> >;
-
-        template<typename T1, typename T2>
-        struct tag_of<std::pair<T1, T2> >;
     }
 
     namespace detail