--- Libc/Libc-391.4.2/include/iso646.h
+++ Libc/Libc-583/include/iso646.h
@@ -29,7 +29,9 @@
 #ifndef _ISO646_H_
 #define	_ISO646_H_
 
-#ifndef _POSIX_C_SOURCE
+#include <sys/cdefs.h>
+
+#if !defined(_POSIX_C_SOURCE) || defined(_DARWIN_C_SOURCE)
 
 #ifndef __cplusplus
 #define	and	&&
@@ -45,6 +47,6 @@
 #define	xor_eq	^=
 #endif /* ! __cplusplus */
 
-#endif /* ! _POSIX_C_SOURCE */
+#endif /* (!_POSIX_C_SOURCE || _DARWIN_C_SOURCE) */
 
 #endif /* !_ISO646_H_ */