diff --git a/newlib/libc/include/stdio.h b/newlib/libc/include/stdio.h
index 9ab5d327b..866d8167d 100644
--- a/newlib/libc/include/stdio.h
+++ b/newlib/libc/include/stdio.h
@@ -164,6 +164,12 @@ typedef _fpos64_t fpos64_t;
 #endif
 #endif
 
+#if __POSIX_VISIBLE
+char *	_EXFUN(ctermid, (char *));
+#endif
+#if __XSI_VISIBLE && __XSI_VISIBLE < 600
+char *	_EXFUN(cuserid, (char *));
+#endif
 FILE *	_EXFUN(tmpfile, (void));
 char *	_EXFUN(tmpnam, (char *));
 #if __BSD_VISIBLE || __XSI_VISIBLE || __POSIX_VISIBLE >= 200112
@@ -728,11 +734,11 @@ _ELIDABLE_INLINE int __sputc_r(struct _reent *_ptr, int _c, FILE *_p) {
 	__swbuf_r(_REENT, (int)(x), p) == EOF : (*(p)->_p = (x), (p)->_p++, 0))
 #endif
 
-#if __XSI_VISIBLE
+#if __GNU_VISIBLE || (__XSI_VISIBLE && __XSI_VISIBLE < 600)
 #define	L_cuserid	9		/* posix says it goes in stdio.h :( */
-#ifdef __CYGWIN__
-#define L_ctermid       16
 #endif
+#if __POSIX_VISIBLE
+#define L_ctermid       16
 #endif
 
 #endif /* !__CUSTOM_FILE_IO__ */
diff --git a/newlib/libc/include/sys/unistd.h b/newlib/libc/include/sys/unistd.h
index c8299bb02..ef00575b5 100644
--- a/newlib/libc/include/sys/unistd.h
+++ b/newlib/libc/include/sys/unistd.h
@@ -31,8 +31,12 @@ int     _EXFUN(close, (int __fildes ));
 #if __POSIX_VISIBLE >= 199209
 size_t	_EXFUN(confstr, (int __name, char *__buf, size_t __len));
 #endif
+#if __XSI_VISIBLE && __XSI_VISIBLE < 700
 char *  _EXFUN(ctermid, (char *__s ));
+#endif
+#if __XSI_VISIBLE && __XSI_VISIBLE < 600
 char *  _EXFUN(cuserid, (char *__s ));
+#endif
 #if __BSD_VISIBLE || (__XSI_VISIBLE && __XSI_VISIBLE < 500)
 int	_EXFUN(daemon, (int nochdir, int noclose));
 #endif