diff --git a/include/boost/endian/detail/endian_reverse.hpp b/include/boost/endian/detail/endian_reverse.hpp
index b619657..5761b2c 100644
--- a/include/boost/endian/detail/endian_reverse.hpp
+++ b/include/boost/endian/detail/endian_reverse.hpp
@@ -16,6 +16,20 @@
 #include <cstddef>
 #include <cstring>
 
+#if defined(BOOST_ENDIAN_NO_INTRINSICS)
+# if defined(BOOST_NO_CXX14_CONSTEXPR)
+#  define BOOST_ENDIAN_CONSTEXPR
+# else
+#  define BOOST_ENDIAN_CONSTEXPR constexpr
+# endif
+#else
+# if defined(BOOST_ENDIAN_CONSTEXPR_INTRINSICS)
+#  define BOOST_ENDIAN_CONSTEXPR BOOST_CONSTEXPR
+# else
+#  define BOOST_ENDIAN_CONSTEXPR
+# endif
+#endif
+
 namespace boost
 {
 namespace endian
@@ -30,12 +44,12 @@ namespace detail
 //  -- intrinsic approach suggested by reviewers, and by David Stone, who provided
 //     his Boost licensed macro implementation (detail/intrinsic.hpp)
 
-inline uint8_t endian_reverse_impl( uint8_t x ) BOOST_NOEXCEPT
+inline uint8_t BOOST_CONSTEXPR endian_reverse_impl( uint8_t x ) BOOST_NOEXCEPT
 {
     return x;
 }
 
-inline uint16_t endian_reverse_impl( uint16_t x ) BOOST_NOEXCEPT
+inline uint16_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl( uint16_t x ) BOOST_NOEXCEPT
 {
 #ifdef BOOST_ENDIAN_NO_INTRINSICS
 
@@ -48,7 +62,7 @@ inline uint16_t endian_reverse_impl( uint16_t x ) BOOST_NOEXCEPT
 #endif
 }
 
-inline uint32_t endian_reverse_impl(uint32_t x) BOOST_NOEXCEPT
+inline uint32_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl(uint32_t x) BOOST_NOEXCEPT
 {
 #ifdef BOOST_ENDIAN_NO_INTRINSICS
 
@@ -62,7 +76,7 @@ inline uint32_t endian_reverse_impl(uint32_t x) BOOST_NOEXCEPT
 #endif
 }
 
-inline uint64_t endian_reverse_impl(uint64_t x) BOOST_NOEXCEPT
+inline uint64_t BOOST_ENDIAN_CONSTEXPR endian_reverse_impl(uint64_t x) BOOST_NOEXCEPT
 {
 #ifdef BOOST_ENDIAN_NO_INTRINSICS
 
diff --git a/include/boost/endian/detail/intrinsic.hpp b/include/boost/endian/detail/intrinsic.hpp
index f110276..d806367 100644
--- a/include/boost/endian/detail/intrinsic.hpp
+++ b/include/boost/endian/detail/intrinsic.hpp
@@ -18,7 +18,7 @@
   #define __has_builtin(x) 0  // Compatibility with non-clang compilers
 #endif
 
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) && ( !defined(__clang__) || defined(__c2__) )
 //  Microsoft documents these as being compatible since Windows 95 and specifically
 //  lists runtime library support since Visual Studio 2003 (aka 7.1).
 //  Clang/c2 uses the Microsoft rather than GCC intrinsics, so we check for
@@ -46,6 +46,8 @@
 # define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_4(x) __builtin_bswap32(x)
 # define BOOST_ENDIAN_INTRINSIC_BYTE_SWAP_8(x) __builtin_bswap64(x)
 
+# define BOOST_ENDIAN_CONSTEXPR_INTRINSICS
+
 //  Linux systems provide the byteswap.h header, with
 #elif defined(__linux__)
 //  don't check for obsolete forms defined(linux) and defined(__linux) on the theory that