Index: iterator.hpp
===================================================================
--- iterator.hpp	(revision 84053)
+++ iterator.hpp	(working copy)
@@ -143,7 +143,6 @@
 struct iterator< ::boost::no_traversal_tag, T, Reference, DifferenceType, ValueType> :
     boost::mpl::vector<
         copy_constructible<T>,
-        constructible<T()>,
         equality_comparable<T>,
         dereferenceable<typename iterator_reference<Reference, ValueType>::type, T>,
         assignable<T>
@@ -173,7 +172,10 @@
 
 template<class T, class Reference, class DifferenceType, class ValueType>
 struct iterator< ::boost::forward_traversal_tag, T, Reference, DifferenceType, ValueType> :
-    iterator< ::boost::incrementable_traversal_tag, T, Reference, DifferenceType, ValueType>
+    boost::mpl::vector<
+        iterator< ::boost::incrementable_traversal_tag, T, Reference, DifferenceType, ValueType>,
+        constructible<T()>
+    >
 {};
 
 template<class T, class Reference, class DifferenceType, class ValueType>