+#if !defined(UTIL_ARCH_LITTLE_ENDIAN) || !defined(UTIL_ARCH_BIG_ENDIAN)
+# error "UTIL_ARCH_LITTLE_ENDIAN and/or UTIL_ARCH_BIG_ENDIAN were unset."
+#elif UTIL_ARCH_LITTLE_ENDIAN == UTIL_ARCH_BIG_ENDIAN
+# error "UTIL_ARCH_LITTLE_ENDIAN and UTIL_ARCH_BIG_ENDIAN must not both be 1 or 0."
+#endif
+