diff --git a/demo-async.c b/demo-async.c
index dd869a8..9d398a7 100644
--- a/demo-async.c
+++ b/demo-async.c
@@ -1,3 +1,6 @@
+// <poll.h> might need this for sigset_t
+#define _XOPEN_SOURCE 600
+
 #include <poll.h>
 #include <stdio.h>