diff --git a/include/boost/integer/integer_mask.hpp b/include/boost/integer/integer_mask.hpp
index 0a092d3..65ee5d5 100644
--- a/include/boost/integer/integer_mask.hpp
+++ b/include/boost/integer/integer_mask.hpp
@@ -15,6 +15,8 @@
 #include <boost/config.hpp>   // for BOOST_STATIC_CONSTANT
 #include <boost/integer.hpp>  // for boost::uint_t
 
+#include <boost/detail/extended_integer.hpp>  // for BOOST_HAS_XINT, etc.
+
 #include <climits>  // for UCHAR_MAX, etc.
 #include <cstddef>  // for std::size_t
 
@@ -84,6 +86,10 @@ BOOST_LOW_BITS_MASK_SPECIALIZE( unsigned int );
 BOOST_LOW_BITS_MASK_SPECIALIZE( unsigned long );
 #endif
 
+#if BOOST_HAS_XINT && (BOOST_UXINT_MAX > ULONG_MAX)
+BOOST_LOW_BITS_MASK_SPECIALIZE( ::boost::detail::uxint_t );
+#endif
+
 #undef BOOST_LOW_BITS_MASK_SPECIALIZE
 
 
diff --git a/include/boost/integer_fwd.hpp b/include/boost/integer_fwd.hpp
index 446ad66..e15385a 100644
--- a/include/boost/integer_fwd.hpp
+++ b/include/boost/integer_fwd.hpp
@@ -155,6 +155,12 @@ template <  >
     struct low_bits_mask_t< ::std::numeric_limits<unsigned long>::digits >;
 #endif
 
+#if BOOST_HAS_XINT && (BOOST_UXINT_MAX > ULONG_MAX)
+template <  >
+    struct low_bits_mask_t< ::std::numeric_limits< ::boost::detail::uxint_t
+     >::digits >;
+#endif
+
 
 //  From <boost/integer/static_log2.hpp>  ------------------------------------//
 
diff --git a/test/integer_mask_test.cpp b/test/integer_mask_test.cpp
index 4444801..99a22b0 100644
--- a/test/integer_mask_test.cpp
+++ b/test/integer_mask_test.cpp
@@ -8,7 +8,8 @@
 //  See http://www.boost.org for most recent version including documentation.
 
 //  Revision History
-//  27 Jul 2008  Changed tests to use the unit-test system (Daryle Walker)
+//  27 Jul 2008  Changed tests to use the unit-test system; added
+//               extended-integer support. (Daryle Walker)
 //  23 Sep 2001  Initial version (Daryle Walker)
 
 #define BOOST_TEST_MODULE  "Integer mask tests"
@@ -16,6 +17,7 @@
 
 #include <boost/cstdint.hpp>               // for boost::uintmax_t
 #include <boost/integer/integer_mask.hpp>  // for boost::high_bit_mask_t, etc.
+#include <boost/limits.hpp>                // for std::numeric_limits
 #include <boost/mpl/assert.hpp>            // for BOOST_MPL_ASSERT_RELATION
 #include <boost/mpl/range_c.hpp>           // for boost::mpl::range_c
 
@@ -30,8 +32,10 @@ namespace
 boost::uintmax_t const  one = 1u;
 
 // List the ranges of template parameters tests (ranges are half-open)
-typedef boost::mpl::range_c<std::size_t, 0u, 32u>  high_bit_offsets;
-typedef boost::mpl::range_c<std::size_t, 1u, 33u>  low_bit_lengths;
+int const  max_offset = std::numeric_limits<boost::uintmax_t>::digits;
+
+typedef boost::mpl::range_c<std::size_t, 0, max_offset>     high_bit_offsets;
+typedef boost::mpl::range_c<std::size_t, 1, max_offset + 1>  low_bit_lengths;
 
 }  // unnamed namespace