diff --git a/lib/ethash/builtins.h b/lib/ethash/builtins.h
index 1d43ba99..e2571841 100644
--- a/lib/ethash/builtins.h
+++ b/lib/ethash/builtins.h
@@ -10,7 +10,7 @@
 
 #pragma once
 
-#ifdef _MSC_VER
+#if defined(_MSC_VER) && !defined(__clang__)
 #include <intrin.h>
 
 #ifdef __cplusplus
diff --git a/lib/ethash/endianness.hpp b/lib/ethash/endianness.hpp
index cdb9750e..cb9ab39e 100644
--- a/lib/ethash/endianness.hpp
+++ b/lib/ethash/endianness.hpp
@@ -1,5 +1,5 @@
 // ethash: C/C++ implementation of Ethash, the Ethereum Proof of Work algorithm.
-// Copyright 2018-2019 Pawel Bylica.
+// Copyright 2018 Pawel Bylica.
 // Licensed under the Apache License, Version 2.0.
 
 /// @file
@@ -11,39 +11,31 @@
 
 #pragma once
 
+#include "../support/attributes.h"
 #include <ethash/ethash.hpp>
 
-#if _WIN32
-
-#include <stdlib.h>
-
-#define bswap32 _byteswap_ulong
-#define bswap64 _byteswap_uint64
-
-// On Windows assume little endian.
-#define __LITTLE_ENDIAN 1234
-#define __BIG_ENDIAN 4321
-#define __BYTE_ORDER __LITTLE_ENDIAN
-
-#elif __APPLE__
-
-#include <machine/endian.h>
-
-#define bswap32 __builtin_bswap32
-#define bswap64 __builtin_bswap64
-
+#ifndef __BYTE_ORDER__
+#if defined(_WIN32)  // On Windows assume little endian.
+#define __ORDER_LITTLE_ENDIAN__ 1234
+#define __ORDER_BIG_ENDIAN__ 4321
+#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
 #else
+#error "Unknown endianness"
+#endif
+#endif
 
-#include <endian.h>
-
+#if __has_builtin(__builtin_bswap64) || defined(__GNUC__)
 #define bswap32 __builtin_bswap32
 #define bswap64 __builtin_bswap64
-
+#elif defined(_MSC_VER)
+#include <stdlib.h>
+#define bswap32 _byteswap_ulong
+#define bswap64 _byteswap_uint64
 #endif
 
 namespace ethash
 {
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 
 struct le
 {
@@ -61,7 +53,7 @@ struct be
 };
 
 
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 
 struct le
 {
@@ -96,4 +88,4 @@ struct be
 };
 
 #endif
-}  // namespace ethash
\ No newline at end of file
+}  // namespace ethash