diff --git a/include/boost/mp11/detail/mp_for_index.hpp b/include/boost/mp11/detail/mp_for_index.hpp
index 85f3c45..88a3293 100644
--- a/include/boost/mp11/detail/mp_for_index.hpp
+++ b/include/boost/mp11/detail/mp_for_index.hpp
@@ -9,10 +9,17 @@
 //  http://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/mp11/integral.hpp>
+#include <boost/config.hpp>
 #include <type_traits>
 #include <utility>
 #include <cassert>
 
+#if !defined( BOOST_NO_CXX14_CONSTEXPR )
+# define BOOST_MP11_CONSTEXPR14 constexpr
+#else
+# define BOOST_MP11_CONSTEXPR14
+#endif
+
 namespace boost
 {
 namespace mp11
@@ -23,7 +30,7 @@ namespace detail
 
 template<std::size_t N> struct mp_for_index_impl_
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -55,7 +62,7 @@ template<> struct mp_for_index_impl_<0>
 
 template<> struct mp_for_index_impl_<1>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         return std::forward<F>(f)( mp_size_t<K+0>() );
     }
@@ -63,7 +70,7 @@ template<> struct mp_for_index_impl_<1>
 
 template<> struct mp_for_index_impl_<2>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -75,7 +82,7 @@ template<> struct mp_for_index_impl_<2>
 
 template<> struct mp_for_index_impl_<3>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -88,7 +95,7 @@ template<> struct mp_for_index_impl_<3>
 
 template<> struct mp_for_index_impl_<4>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -102,7 +109,7 @@ template<> struct mp_for_index_impl_<4>
 
 template<> struct mp_for_index_impl_<5>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -117,7 +124,7 @@ template<> struct mp_for_index_impl_<5>
 
 template<> struct mp_for_index_impl_<6>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -133,7 +140,7 @@ template<> struct mp_for_index_impl_<6>
 
 template<> struct mp_for_index_impl_<7>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -150,7 +157,7 @@ template<> struct mp_for_index_impl_<7>
 
 template<> struct mp_for_index_impl_<8>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -168,7 +175,7 @@ template<> struct mp_for_index_impl_<8>
 
 template<> struct mp_for_index_impl_<9>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -187,7 +194,7 @@ template<> struct mp_for_index_impl_<9>
 
 template<> struct mp_for_index_impl_<10>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -207,7 +214,7 @@ template<> struct mp_for_index_impl_<10>
 
 template<> struct mp_for_index_impl_<11>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -228,7 +235,7 @@ template<> struct mp_for_index_impl_<11>
 
 template<> struct mp_for_index_impl_<12>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -250,7 +257,7 @@ template<> struct mp_for_index_impl_<12>
 
 template<> struct mp_for_index_impl_<13>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -273,7 +280,7 @@ template<> struct mp_for_index_impl_<13>
 
 template<> struct mp_for_index_impl_<14>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -297,7 +304,7 @@ template<> struct mp_for_index_impl_<14>
 
 template<> struct mp_for_index_impl_<15>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -322,7 +329,7 @@ template<> struct mp_for_index_impl_<15>
 
 template<> struct mp_for_index_impl_<16>
 {
-    template<std::size_t K, class F> static decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
+    template<std::size_t K, class F> static BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) call( std::size_t i, F && f )
     {
         switch( i )
         {
@@ -348,17 +355,19 @@ template<> struct mp_for_index_impl_<16>
 
 } // namespace detail
 
-template<std::size_t N, class F> inline decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) mp_for_index( std::size_t i, F && f )
+template<std::size_t N, class F> inline BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) mp_for_index( std::size_t i, F && f )
 {
     assert( i < N );
     return detail::mp_for_index_impl_<N>::template call<0>( i, std::forward<F>(f) );
 }
 
-template<class N, class F> inline decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) mp_for_index( std::size_t i, F && f )
+template<class N, class F> inline BOOST_MP11_CONSTEXPR14 decltype(std::declval<F>()(std::declval<mp_size_t<0>>())) mp_for_index( std::size_t i, F && f )
 {
     return mp_for_index<N::value>( i, std::forward<F>(f) );
 }
 
+#undef BOOST_MP11_CONSTEXPR14
+
 } // namespace mp11
 } // namespace boost
 
diff --git a/test/Jamfile.v2 b/test/Jamfile.v2
index c9b8fc8..f5c3753 100644
--- a/test/Jamfile.v2
+++ b/test/Jamfile.v2
@@ -72,6 +72,7 @@ run mp_for_each.cpp : : : $(REQ) ;
 run mp_insert.cpp : : : $(REQ) ;
 run mp_erase.cpp : : : $(REQ) ;
 run mp_for_index.cpp : : : $(REQ) ;
+run mp_for_index_cx.cpp : : : $(REQ) ;
 
 # integral
 run integral.cpp : : : $(REQ) ;
diff --git a/test/mp_for_index_cx.cpp b/test/mp_for_index_cx.cpp
new file mode 100644
index 0000000..db8d180
--- /dev/null
+++ b/test/mp_for_index_cx.cpp
@@ -0,0 +1,41 @@
+
+// Copyright 2017 Peter Dimov.
+//
+// Distributed under the Boost Software License, Version 1.0.
+//
+// See accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/config.hpp>
+
+#if defined( BOOST_NO_CXX14_CONSTEXPR )
+
+int main() {}
+
+#else
+
+#include <boost/mp11/algorithm.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/detail/workaround.hpp>
+
+using boost::mp11::mp_size_t;
+using boost::mp11::mp_for_index;
+
+struct F
+{
+    template<std::size_t I> constexpr std::size_t operator()( mp_size_t<I> ) const
+    {
+        return I;
+    }
+};
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    constexpr std::size_t i = mp_for_index<64>( 57, F{} );
+    STATIC_ASSERT( i == 57 );
+}
+
+#endif