diff --git a/src/core/delete.c b/src/core/delete.c
index e59101a82..fae704bdc 100644
--- a/src/core/delete.c
+++ b/src/core/delete.c
@@ -22,8 +22,7 @@
  * 02111-1307, USA.
  */
 
-#define _GNU_SOURCE
-#define _SVID_SOURCE /* for gethostname() */
+#define _XOPEN_SOURCE /* for kill() */
 
 #include <config.h>
 #include "util.h"
diff --git a/src/core/display.c b/src/core/display.c
index 9fedf0a8e..24d25966b 100644
--- a/src/core/display.c
+++ b/src/core/display.c
@@ -30,6 +30,8 @@
  * The display is represented as a MetaDisplay struct.
  */
 
+#define _XOPEN_SOURCE 600 /* for gethostname() */
+
 #include <config.h>
 #include "display-private.h"
 #include "util.h"