diff --git a/include/boost/mpl/arg.hpp b/include/boost/mpl/arg.hpp
index 2af8d46..7690f6d 100644
--- a/include/boost/mpl/arg.hpp
+++ b/include/boost/mpl/arg.hpp
@@ -106,6 +106,7 @@ template<> struct arg<i>
     {
         typedef BOOST_PP_CAT(U,i) type;
 #if !defined(__BORLANDC__) || (__BORLANDC__ > 0x561 && defined(BOOST_STRICT_CONFIG))
+     private:
         BOOST_STATIC_CONSTANT(bool, nv = !is_void_<type>::value);
         BOOST_STATIC_ASSERT(nv);
 #endif
@@ -128,6 +129,7 @@ template<> struct arg<-1>
     {
         typedef U1 type;
 #if !defined(__BORLANDC__) || (__BORLANDC__ > 0x561 && defined(BOOST_STRICT_CONFIG))
+     private:
         BOOST_STATIC_CONSTANT(bool, nv = !is_void_<type>::value);
         BOOST_STATIC_ASSERT(nv);
 #endif
diff --git a/include/boost/mpl/aux_/preprocessed/plain/arg.hpp b/include/boost/mpl/aux_/preprocessed/plain/arg.hpp
index e3c94c5..df227a9 100644
--- a/include/boost/mpl/aux_/preprocessed/plain/arg.hpp
+++ b/include/boost/mpl/aux_/preprocessed/plain/arg.hpp
@@ -33,6 +33,7 @@ template<> struct arg<1>
     struct apply
     {
         typedef U1 type;
+     private:
         BOOST_STATIC_CONSTANT(bool, nv = !is_void_<type>::value);
         BOOST_STATIC_ASSERT(nv);
     };
@@ -50,6 +51,7 @@ template<> struct arg<2>
     struct apply
     {
         typedef U2 type;
+     private:
         BOOST_STATIC_CONSTANT(bool, nv = !is_void_<type>::value);
         BOOST_STATIC_ASSERT(nv);
     };
@@ -67,6 +69,7 @@ template<> struct arg<3>
     struct apply
     {
         typedef U3 type;
+     private:
         BOOST_STATIC_CONSTANT(bool, nv = !is_void_<type>::value);
         BOOST_STATIC_ASSERT(nv);
     };
@@ -84,6 +87,7 @@ template<> struct arg<4>
     struct apply
     {
         typedef U4 type;
+     private:
         BOOST_STATIC_CONSTANT(bool, nv = !is_void_<type>::value);
         BOOST_STATIC_ASSERT(nv);
     };
@@ -101,6 +105,7 @@ template<> struct arg<5>
     struct apply
     {
         typedef U5 type;
+     private:
         BOOST_STATIC_CONSTANT(bool, nv = !is_void_<type>::value);
         BOOST_STATIC_ASSERT(nv);
     };