diff --git a/include/boost/core/bit.hpp b/include/boost/core/bit.hpp
index 6029ba5..5612f71 100644
--- a/include/boost/core/bit.hpp
+++ b/include/boost/core/bit.hpp
@@ -241,6 +241,15 @@ inline int countl_impl( boost::uint64_t x ) BOOST_NOEXCEPT
     }
 }
 
+#elif defined(_MSC_VER) && defined(BOOST_CORE_HAS_BUILTIN_ISCONSTEVAL)
+
+BOOST_CXX14_CONSTEXPR inline int countl_impl( boost::uint64_t x ) BOOST_NOEXCEPT
+{
+    return static_cast<boost::uint32_t>( x >> 32 ) != 0?
+        boost::core::detail::countl_impl( static_cast<boost::uint32_t>( x >> 32 ) ):
+        boost::core::detail::countl_impl( static_cast<boost::uint32_t>( x ) ) + 32;
+}
+
 #else
 
 inline int countl_impl( boost::uint64_t x ) BOOST_NOEXCEPT
@@ -457,6 +466,15 @@ inline int countr_impl( boost::uint64_t x ) BOOST_NOEXCEPT
     }
 }
 
+#elif defined(_MSC_VER) && defined(BOOST_CORE_HAS_BUILTIN_ISCONSTEVAL)
+
+BOOST_CXX14_CONSTEXPR inline int countr_impl( boost::uint64_t x ) BOOST_NOEXCEPT
+{
+    return static_cast<boost::uint32_t>( x ) != 0?
+        boost::core::detail::countr_impl( static_cast<boost::uint32_t>( x ) ):
+        boost::core::detail::countr_impl( static_cast<boost::uint32_t>( x >> 32 ) ) + 32;
+}
+
 #else
 
 inline int countr_impl( boost::uint64_t x ) BOOST_NOEXCEPT