diff --git a/opensshlib/xmalloc.c b/opensshlib/xmalloc.c
index b3b8de7..1f64ead 100644
--- a/opensshlib/xmalloc.c
+++ b/opensshlib/xmalloc.c
@@ -13,6 +13,7 @@
  * called by a name other than "ssh" or "Secure Shell".
  */
 
+#define _GNU_SOURCE
 #include "includes.h"
 
 #include <stdarg.h>