#elif HAVE_LITTLE_ENDIAN && HAVE_BIG_ENDIAN
#error "Can't compile for both big and little endian."
#elif HAVE_LITTLE_ENDIAN
+#ifndef __BYTE_ORDER
#define __BYTE_ORDER __LITTLE_ENDIAN
+#elif __BYTE_ORDER != __LITTLE_ENDIAN
+#error "__BYTE_ORDER already defined, but not equal to __LITTLE_ENDIAN"
+#endif
#elif HAVE_BIG_ENDIAN
+#ifndef __BYTE_ORDER
#define __BYTE_ORDER __BIG_ENDIAN
+#elif __BYTE_ORDER != __BIG_ENDIAN
+#error "__BYTE_ORDER already defined, but not equal to __BIG_ENDIAN"
+#endif
#endif