diff --git a/include/boost/iterator/detail/categories.hpp b/include/boost/iterator/detail/categories.hpp
index 48d1e3d..2e53fb6 100644
--- a/include/boost/iterator/detail/categories.hpp
+++ b/include/boost/iterator/detail/categories.hpp
@@ -329,6 +329,25 @@ namespace boost
     template <> struct minimum_category<int, int> { typedef minimum_category type; };
 # endif
 
+    //
+    // Tag classification for use in iterator_adaptor
+    //
+    template <class Tag>
+    struct is_access_tag
+      : mpl::or_<
+            is_tag<readable_iterator_tag, Tag>
+          , mpl::or_< 
+                is_tag<writable_iterator_tag, Tag>
+              , is_tag<swappable_iterator_tag, Tag>
+            >
+        >
+    {};
+
+    template <class Tag>
+    struct is_traversal_tag
+      : is_tag<incrementable_traversal_tag, Tag>
+    {};
+
   } // namespace detail
 
 } // namespace boost
diff --git a/include/boost/iterator/filter_iterator.hpp b/include/boost/iterator/filter_iterator.hpp
index 390dc8e..cd490dc 100644
--- a/include/boost/iterator/filter_iterator.hpp
+++ b/include/boost/iterator/filter_iterator.hpp
@@ -15,34 +15,25 @@
 
 namespace boost
 {
-  namespace detail
-  {
-    template <class Iterator>
-    struct filter_iterator_category
-    {
-       typedef iterator_tag<
-           typename access_category<Iterator>::type
-         , typename minimum_category<
-               bidirectional_traversal_tag
-             , typename traversal_category<Iterator>::type
-           >::type 
-       > type;
-    };
-
-  } // namespace detail
 
   template <class Predicate, class Iterator>
   class filter_iterator
       : public iterator_adaptor<
             filter_iterator<Predicate, Iterator>, Iterator
           , use_default
-          , typename detail::filter_iterator_category<Iterator>::type
+          , typename detail::minimum_category<
+                bidirectional_traversal_tag
+              , typename traversal_category<Iterator>::type
+            >::type 
         >
   {
       typedef iterator_adaptor<
             filter_iterator<Predicate, Iterator>, Iterator
           , use_default
-          , typename detail::filter_iterator_category<Iterator>::type
+          , typename detail::minimum_category<
+                bidirectional_traversal_tag
+              , typename traversal_category<Iterator>::type
+            >::type 
         > super_t;
 
       friend class iterator_core_access;
diff --git a/include/boost/iterator/iterator_adaptor.hpp b/include/boost/iterator/iterator_adaptor.hpp
index faecc1a..af14283 100644
--- a/include/boost/iterator/iterator_adaptor.hpp
+++ b/include/boost/iterator/iterator_adaptor.hpp
@@ -148,9 +148,18 @@ namespace boost
     >
     struct iterator_adaptor_base
     {
-     private: // intermediate results
-        typedef typename detail::ia_dflt_help<
-           Category, BOOST_ITERATOR_CATEGORY<Base>
+    private: // intermediate results
+
+        typedef typename mpl::apply_if<
+            mpl::or_< 
+                is_same<Category, use_default>
+              , mpl::or_<
+                    is_access_tag<Category>
+                  , is_traversal_tag<Category>
+                >
+            >
+          , BOOST_ITERATOR_CATEGORY<Base>
+          , mpl::identity<Category>
         >::type category;
 
         typedef typename detail::ia_dflt_help<
@@ -170,9 +179,17 @@ namespace boost
                 Value, iterator_value<Base>
             >::type
                 
-          , typename access_category_tag<category, reference>::type
-                
-          , typename traversal_category_tag<category>::type
+         , typename mpl::apply_if<
+               is_access_tag<Category>
+             , mpl::identity<Category>
+             , access_category_tag<category, reference>
+           >::type
+
+         , typename mpl::apply_if<
+               is_traversal_tag<Category>
+             , mpl::identity<Category>
+             , traversal_category_tag<category>
+           >::type
                 
           , reference
                 
diff --git a/include/boost/iterator/transform_iterator.hpp b/include/boost/iterator/transform_iterator.hpp
index f281b82..cb41f07 100644
--- a/include/boost/iterator/transform_iterator.hpp
+++ b/include/boost/iterator/transform_iterator.hpp
@@ -90,10 +90,7 @@ namespace boost
       transform_iterator<UnaryFunction, Iterator, Reference, Value>
         , Iterator
         , cv_value_type  
-        , iterator_tag<
-             access_category
-           , typename traversal_category<Iterator>::type
-          >
+        , access_category
         , result_type  
       > type;
     };
diff --git a/test/iterator_adaptor_test.cpp b/test/iterator_adaptor_test.cpp
index 32edd85..5c471d7 100644
--- a/test/iterator_adaptor_test.cpp
+++ b/test/iterator_adaptor_test.cpp
@@ -112,6 +112,17 @@ public:
   {}
 };
 
+// Non-functional iterator for category modification checking
+template <class Iter, class Category>
+struct modify_category 
+  :  boost::iterator_adaptor<
+         modify_category<Iter, Category>
+       , Iter
+       , boost::use_default
+       , Category
+     >
+{};
+  
 template <class T>
 struct fwd_iterator
   : boost::iterator_adaptor<
@@ -221,6 +232,15 @@ main()
 
     test = static_assert_same<BaseIter::iterator_category::access, boost::writable_lvalue_iterator_tag>::value;
     test = static_assert_same<Iter::iterator_category::access, boost::readable_lvalue_iterator_tag>::value;
+  
+    // Test category modification
+    typedef modify_category<BaseIter, boost::readable_iterator_tag> ReadableIter;
+    test = static_assert_same<ReadableIter::iterator_category::access, boost::readable_iterator_tag>::value;
+
+    typedef modify_category<BaseIter, boost::incrementable_traversal_tag> IncrementableIter;
+    test = static_assert_same<BaseIter::iterator_category::traversal, boost::random_access_traversal_tag>::value;
+    test = static_assert_same<IncrementableIter::iterator_category::traversal, boost::incrementable_traversal_tag>::value;
+
   }
   
   // Test the iterator_adaptor
diff --git a/test/unit_tests.cpp b/test/unit_tests.cpp
index 4887357..622d9a7 100644
--- a/test/unit_tests.cpp
+++ b/test/unit_tests.cpp
@@ -91,6 +91,25 @@ void category_test()
         std::output_iterator_tag,std::random_access_iterator_tag, std::output_iterator_tag
     >::value;
     
+    BOOST_STATIC_ASSERT((is_traversal_tag< incrementable_traversal_tag >::value));
+    BOOST_STATIC_ASSERT((is_traversal_tag< single_pass_traversal_tag   >::value));
+    BOOST_STATIC_ASSERT((is_traversal_tag< forward_traversal_tag       >::value));
+    BOOST_STATIC_ASSERT((is_traversal_tag< bidirectional_traversal_tag >::value));
+    BOOST_STATIC_ASSERT((is_traversal_tag< random_access_traversal_tag >::value));
+
+    BOOST_STATIC_ASSERT((!is_traversal_tag< std::input_iterator_tag >::value));
+    BOOST_STATIC_ASSERT((!is_traversal_tag< readable_iterator_tag   >::value));
+
+    BOOST_STATIC_ASSERT((is_access_tag< readable_iterator_tag          >::value));
+    BOOST_STATIC_ASSERT((is_access_tag< writable_iterator_tag          >::value));
+    BOOST_STATIC_ASSERT((is_access_tag< swappable_iterator_tag         >::value));
+    BOOST_STATIC_ASSERT((is_access_tag< readable_writable_iterator_tag >::value));
+    BOOST_STATIC_ASSERT((is_access_tag< readable_lvalue_iterator_tag   >::value));
+    BOOST_STATIC_ASSERT((is_access_tag< writable_lvalue_iterator_tag   >::value));
+
+    BOOST_STATIC_ASSERT((!is_access_tag< std::input_iterator_tag     >::value));
+    BOOST_STATIC_ASSERT((!is_access_tag< incrementable_traversal_tag >::value));
+
     (void)test;
 }