diff --git a/portable_endian.h b/portable_endian.h
new file mode 100644
index 0000000..4db1ae7
--- /dev/null
+++ b/portable_endian.h
@@ -0,0 +1,125 @@
+// taken from
+// https://gist.githubusercontent.com/PkmX/63dd23f28ba885be53a5/raw/c89538c921f08f8dbb5bc5957c871060c720605a/portable_endian.h
+// as of June 11, 2020
+
+// "License": Public Domain
+// I, Mathias Panzenb�ck, place this file hereby into the public domain. Use it at your own risk for whatever you like.
+// In case there are jurisdictions that don't support putting things in the public domain you can also consider it to
+// be "dual licensed" under the BSD, MIT and Apache licenses, if you want to. This code is trivial anyway. Consider it
+// an example on how to get the endian conversion functions on different platforms.
+
+#ifndef PORTABLE_ENDIAN_H__
+#define PORTABLE_ENDIAN_H__
+
+#if (defined(_WIN16) || defined(_WIN32) || defined(_WIN64)) && !defined(__WINDOWS__)
+
+#	define __WINDOWS__
+
+#endif
+
+#if defined(__linux__) || defined(__CYGWIN__)
+
+#	include <endian.h>
+
+#elif defined(__APPLE__)
+
+#	include <libkern/OSByteOrder.h>
+
+#	define htobe16(x) OSSwapHostToBigInt16(x)
+#	define htole16(x) OSSwapHostToLittleInt16(x)
+#	define be16toh(x) OSSwapBigToHostInt16(x)
+#	define le16toh(x) OSSwapLittleToHostInt16(x)
+
+#	define htobe32(x) OSSwapHostToBigInt32(x)
+#	define htole32(x) OSSwapHostToLittleInt32(x)
+#	define be32toh(x) OSSwapBigToHostInt32(x)
+#	define le32toh(x) OSSwapLittleToHostInt32(x)
+
+#	define htobe64(x) OSSwapHostToBigInt64(x)
+#	define htole64(x) OSSwapHostToLittleInt64(x)
+#	define be64toh(x) OSSwapBigToHostInt64(x)
+#	define le64toh(x) OSSwapLittleToHostInt64(x)
+
+#	define __BYTE_ORDER    BYTE_ORDER
+#	define __BIG_ENDIAN    BIG_ENDIAN
+#	define __LITTLE_ENDIAN LITTLE_ENDIAN
+#	define __PDP_ENDIAN    PDP_ENDIAN
+
+#elif defined(__OpenBSD__)
+
+#	include <sys/endian.h>
+
+#elif defined(__NetBSD__) || defined(__FreeBSD__) || defined(__DragonFly__)
+
+#	include <sys/endian.h>
+
+#	define be16toh(x) betoh16(x)
+#	define le16toh(x) letoh16(x)
+
+#	define be32toh(x) betoh32(x)
+#	define le32toh(x) letoh32(x)
+
+#	define be64toh(x) betoh64(x)
+#	define le64toh(x) letoh64(x)
+
+#elif defined(__WINDOWS__)
+
+#	include <windows.h>
+
+#	if BYTE_ORDER == LITTLE_ENDIAN
+
+#               if defined(_MSC_VER)
+#                       include <stdlib.h>
+#			define htobe16(x) _byteswap_ushort(x)
+#			define htole16(x) (x)
+#			define be16toh(x) _byteswap_ushort(x)
+#			define le16toh(x) (x)
+
+#			define htobe32(x) _byteswap_ulong(x)
+#			define htole32(x) (x)
+#			define be32toh(x) _byteswap_ulong(x)
+#			define le32toh(x) (x)
+
+#			define htobe64(x) _byteswap_uint64(x)
+#			define htole64(x) (x)
+#			define be64toh(x) _byteswap_uint64(x)
+#			define le64toh(x) (x)
+
+#               elif defined(__GNUC__) || defined(__clang__)
+
+#			define htobe16(x) __builtin_bswap16(x)
+#			define htole16(x) (x)
+#			define be16toh(x) __builtin_bswap16(x)
+#			define le16toh(x) (x)
+
+#			define htobe32(x) __builtin_bswap32(x)
+#			define htole32(x) (x)
+#			define be32toh(x) __builtin_bswap32(x)
+#			define le32toh(x) (x)
+
+#			define htobe64(x) __builtin_bswap64(x)
+#			define htole64(x) (x)
+#			define be64toh(x) __builtin_bswap64(x)
+#			define le64toh(x) (x)
+#               else
+#                       error platform not supported
+#               endif
+
+#	else
+
+#		error byte order not supported
+
+#	endif
+
+#	define __BYTE_ORDER    BYTE_ORDER
+#	define __BIG_ENDIAN    BIG_ENDIAN
+#	define __LITTLE_ENDIAN LITTLE_ENDIAN
+#	define __PDP_ENDIAN    PDP_ENDIAN
+
+#else
+
+#	error platform not supported
+
+#endif
+
+#endif
diff --git a/speck.c b/speck.c
index 23aefd7..d9afca5 100644
--- a/speck.c
+++ b/speck.c
@@ -2,13 +2,12 @@
 // taken from (and modified: removed pure crypto-stream generation and seperated key expansion)
 // https://github.com/nsacyber/simon-speck-supercop/blob/master/crypto_stream/speck128256ctr/
 
-#include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
+#include "portable_endian.h"
 
 #include "speck.h"
 
-
 #if defined (__AVX2__)	// AVX support ----------------------------------------------------
 
 
@@ -682,6 +681,8 @@ int speck_test () {
 }
 
 /*
+#include <stdio.h> // for testing
+
   int main (int argc, char* argv[]) {
 
   fprintf (stdout, "SPECK SELF TEST RESULT: %u\n", speck_test (0,NULL));
diff --git a/speck.h b/speck.h
index ff92a5f..18a67b6 100644
--- a/speck.h
+++ b/speck.h
@@ -2,11 +2,6 @@
 // taken from (and modified: removed pure crypto-stream generation and seperated key expansion)
 // https://github.com/nsacyber/simon-speck-supercop/blob/master/crypto_stream/speck128256ctr/
 
-#ifdef __APPLE__
-#include <libkern/OSByteOrder.h>
-#define htole64(x) OSSwapHostToLittleInt64(x)
-#endif
-
 #define u32 uint32_t
 #define u64 uint64_t