Personally, I'd like to see some extra protection at the beginning of all the detection. Surround the current implementation with... #if !defined (BOOST_BIG_ENDIAN) \ && !defined (BOOST_LITTLE_ENDIAN) \ && !defined (BOOST_PDP_ENDIAN) // Insert current implementation here... #endif Also, some protection at the end of the file, in case someone mistakenly "adds" something incorrect, or incorrectly makes a definition on the command line... // Check for some consistency #if defined (BOOST_BIG_ENDIAN) # if !(BOOST_BYTE_ORDER == 4321) # error BOOST_BYTE_ORDER must be 4321 for BOOST_BIG_ENDIAN # endif # if defined (BOOST_LITTLE_ENDIAN) || defined (BOOST_PDP_ENDIAN) # error Multiple BOOST_endian definitions # endif #elif defined (BOOST_LITTLE_ENDIAN) # if !(BOOST_BYTE_ORDER == 1234) # error BOOST_BYTE_ORDER must be 1234 for BOOST_LITTLE_ENDIAN # endif # if defined (BOOST_PDP_ENDIAN) # error Multiple BOOST_endian definitions # endif #elif defined (BOOST_PDP_ENDIAN) # if !(BOOST_BYTE_ORDER == 3412) # error BOOST_BYTE_ORDER must be 3412 for BOOST_PDP_ENDIAN # endif #else # error Missing a definition for the proper endian #endif