diff -urb -x .svn trunk/boost/mpl/string.hpp trunk_patched/boost/mpl/string.hpp
--- trunk/boost/mpl/string.hpp	2009-04-18 17:43:51.000000000 +0400
+++ trunk_patched/boost/mpl/string.hpp	2009-04-18 17:41:21.000000000 +0400
@@ -26,6 +26,7 @@
 #include <boost/mpl/back_inserter.hpp>
 #include <boost/mpl/front_inserter.hpp>
 #include <boost/mpl/iterator_range.hpp>
+#include <boost/mpl/empty.hpp>
 #include <boost/preprocessor/arithmetic/dec.hpp>
 #include <boost/preprocessor/arithmetic/add.hpp>
 #include <boost/preprocessor/arithmetic/div.hpp>
@@ -243,12 +244,6 @@
             type;
         };
 
-        template<typename Value>
-        struct apply<mpl::string<>, Value, false>
-        {
-            typedef mpl::string<(char)Value::value> type;
-        };
-
         #define M0(z,n,data)                                                                        \
         template<BOOST_PP_ENUM_PARAMS_Z(z, n, unsigned C), typename Value>                          \
         struct apply<mpl::string<BOOST_PP_ENUM_PARAMS_Z(z, n, C)>, Value, true>                     \
@@ -268,10 +263,14 @@
         struct apply<mpl::string<BOOST_PP_ENUM_PARAMS(BOOST_MPL_STRING_MAX_PARAMS, C)>, Value, false>
         {
             typedef
-                mpl::string<
+                typename mpl::if_<
+                    mpl::empty<mpl::string<BOOST_PP_ENUM_PARAMS(BOOST_MPL_STRING_MAX_PARAMS, C)> >
+                  , mpl::string<(char)Value::value>
+                  , mpl::string<
                     ((((unsigned char)Value::value)<<(BOOST_MPL_MULTICHAR_LENGTH(C0)*8))|C0)
                   , BOOST_PP_ENUM_SHIFTED_PARAMS(BOOST_MPL_STRING_MAX_PARAMS, C)
                 >
+                >::type
             type;
         };
     };
diff -urb -x .svn trunk/libs/mpl/test/string.cpp trunk_patched/libs/mpl/test/string.cpp
--- trunk/libs/mpl/test/string.cpp	2009-04-18 17:43:51.000000000 +0400
+++ trunk_patched/libs/mpl/test/string.cpp	2009-04-18 17:39:47.000000000 +0400
@@ -293,6 +293,9 @@
         BOOST_MPL_ASSERT((boost::is_same<t7, mpl::string<'aaaa','aaaa','aaaX'> >));
     }
 
+	BOOST_MPL_ASSERT((mpl::empty<mpl::string<> >));
+	BOOST_MPL_ASSERT_NOT((mpl::empty<mpl::string<'hi!'> >));
+
     // testing push_front
     {
         typedef mpl::push_front<mpl::string<>, mpl::char_<'a'> >::type t1;
@@ -343,9 +346,6 @@
     mpl::for_each<mpl::string<'Hell','o wo','rld!'> >(push_char(result));
     BOOST_TEST("Hello world!" == result);
 
-    BOOST_MPL_ASSERT((mpl::empty<mpl::string<> >));
-    BOOST_MPL_ASSERT_NOT((mpl::empty<mpl::string<'hi!'> >));
-
     BOOST_TEST(('h' == mpl::front<mpl::string<'hi!'> >::type()));
     BOOST_TEST(('!' == mpl::back<mpl::string<'hi!'> >::type()));