diff --git a/include/boost/detail/utf8_codecvt_facet.hpp b/include/boost/detail/utf8_codecvt_facet.hpp
index afe3f2c..12ae19b 100644
--- a/include/boost/detail/utf8_codecvt_facet.hpp
+++ b/include/boost/detail/utf8_codecvt_facet.hpp
@@ -179,7 +179,7 @@ protected:
     // How many char objects can I process to get <= max_limit
     // wchar_t objects?
     virtual int do_length(
-        const std::mbstate_t &,
+        std::mbstate_t &,
         const char * from,
         const char * from_end, 
         std::size_t max_limit
@@ -189,8 +189,9 @@ protected:
 #endif
     ;
 
+    // Nonstandard override
     virtual int do_length(
-        std::mbstate_t & s,
+        const std::mbstate_t & s,
         const char * from,
         const char * from_end, 
         std::size_t max_limit
@@ -200,7 +201,7 @@ protected:
 #endif
     {
         return do_length(
-            const_cast<const std::mbstate_t &>(s),
+            const_cast<std::mbstate_t &>(s),
             from,
             from_end,
             max_limit
diff --git a/include/boost/detail/utf8_codecvt_facet.ipp b/include/boost/detail/utf8_codecvt_facet.ipp
index 902bd2e..d60f906 100644
--- a/include/boost/detail/utf8_codecvt_facet.ipp
+++ b/include/boost/detail/utf8_codecvt_facet.ipp
@@ -177,7 +177,7 @@ std::codecvt_base::result utf8_codecvt_facet::do_out(
 // How many char objects can I process to get <= max_limit
 // wchar_t objects?
 int utf8_codecvt_facet::do_length(
-    const std::mbstate_t &,
+    std::mbstate_t &,
     const char * from,
     const char * from_end, 
     std::size_t max_limit