Index: whois-5.5.18/mkpasswd.c
===================================================================
--- whois-5.5.18.orig/mkpasswd.c
+++ whois-5.5.18/mkpasswd.c
@@ -19,10 +19,7 @@
  */
 
 /* for crypt, snprintf and strcasecmp */
-#define _XOPEN_SOURCE 500
-#define _BSD_SOURCE 1
 #define _DEFAULT_SOURCE 1
-#define __EXTENSIONS__ 1
 
 /* System library */
 #include <stdio.h>
Index: whois-5.5.18/whois.c
===================================================================
--- whois-5.5.18.orig/whois.c
+++ whois-5.5.18/whois.c
@@ -9,9 +9,6 @@
  * SPDX-License-Identifier: GPL-2.0-or-later
  */
 
-/* for AI_IDN */
-#define _GNU_SOURCE
-
 /* System library */
 #include <stdio.h>
 #include <stdlib.h>
Index: whois-5.5.18/Makefile
===================================================================
--- whois-5.5.18.orig/Makefile
+++ whois-5.5.18/Makefile
@@ -70,7 +70,7 @@ else
 mkpasswd_LDADD += -lcrypt
 endif
 
-CPPFLAGS += $(DEFS) $(INCLUDES)
+CPPFLAGS += -D_GNU_SOURCE $(DEFS) $(INCLUDES)
 
 BASHCOMPDIR ?= $(shell $(PKG_CONFIG) --variable=completionsdir bash-completion 2>/dev/null || echo /etc/bash_completion.d)