-#if !defined(__BYTE_ORDER)
-# if defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
-# define __BYTE_ORDER BYTE_ORDER
-# define __LITTLE_ENDIAN LITTLE_ENDIAN
-# define __BIG_ENDIAN BIG_ENDIAN
+#if defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
+
+# define GIT_BYTE_ORDER BYTE_ORDER
+# define GIT_LITTLE_ENDIAN LITTLE_ENDIAN
+# define GIT_BIG_ENDIAN BIG_ENDIAN
+
+#elif defined(__BYTE_ORDER) && defined(__LITTLE_ENDIAN) && defined(__BIG_ENDIAN)
+
+# define GIT_BYTE_ORDER __BYTE_ORDER
+# define GIT_LITTLE_ENDIAN __LITTLE_ENDIAN
+# define GIT_BIG_ENDIAN __BIG_ENDIAN
+
+#else
+
+# define GIT_BIG_ENDIAN 4321
+# define GIT_LITTLE_ENDIAN 1234
+
+# if defined(_BIG_ENDIAN) && !defined(_LITTLE_ENDIAN)
+# define GIT_BYTE_ORDER GIT_BIG_ENDIAN
+# elif defined(_BIG_ENDIAN) && !defined(_LITTLE_ENDIAN)
+# define GIT_BYTE_ORDER GIT_LITTLE_ENDIAN
+# else
+# error "Cannot determine endianness"