-struct group *getgrgid __P((gid_t));
-struct group *getgrnam __P((const char *));
-int getgrgid_r __P((gid_t, struct group *, char *, size_t, struct group **));
-int getgrnam_r __P((const char *, struct group *, char *, size_t, struct group **));
-#ifndef _POSIX_SOURCE
-struct group *getgrent __P((void));
-int setgrent __P((void));
-void endgrent __P((void));
-void setgrfile __P((const char *));
-int setgroupent __P((int));
+/* [XBD] */
+struct group *getgrgid(gid_t);
+struct group *getgrnam(const char *);
+/* [TSF] */
+int getgrgid_r(gid_t, struct group *, char *, size_t, struct group **);
+int getgrnam_r(const char *, struct group *, char *, size_t, struct group **);
+/* [XSI] */
+struct group *getgrent(void);
+int setgrent(void);
+void endgrent(void);
+
+#ifndef _POSIX_C_SOURCE
+#ifndef _XOPEN_SOURCE
+char *group_from_gid(gid_t, int);
+#endif
+void setgrfile(const char *);
+int setgroupent(int);