#define R_OK 4
#endif
-// there is no distinction between text and binary files under Unix
-#ifdef __UNIX__
+// there is no distinction between text and binary files under Unix, so define
+// O_BINARY as 0 if the system headers don't do it already
+#if defined(__UNIX__) && !defined(O_BINARY)
#define O_BINARY (0)
#endif //__UNIX__