/// _WIN32 Building on Windows (any)
/// _WIN64 Building on Windows 64 bit
-#if defined(_WIN64) && !defined(IS_64BIT) // Last condition means Makefile is not used
+#if defined(_WIN64) && defined(_MSC_VER) // No Makefile used
# include <intrin.h> // MSVC popcnt and bsfq instrinsics
# define IS_64BIT
# define USE_BSFQ