#elif defined(__CYGWIN__) || defined(__CYGWIN32__)
# define OS_CYGWIN
#elif defined(linux) || defined(__linux) || defined(__linux__)
-# define OS_LINUX
+# ifndef OS_LINUX
+# define OS_LINUX
+# endif
#elif defined(macintosh) || defined(__APPLE__) || defined(__APPLE_CC__)
# define OS_MACOSX
#elif defined(__FreeBSD__)