diff --git a/src/ptmx.c b/src/ptmx.c
index 8f8c654..0bc3ab5 100644
--- a/src/ptmx.c
+++ b/src/ptmx.c
@@ -1,5 +1,4 @@
-#define _XOPEN_SOURCE
-#define _XOPEN_SOURCE_EXTENDED
+#define _GNU_SOURCE
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>