diff --git a/sys/net/if_tun.h b/sys/net/if_tun.h
index 6c44fcdc75ae..128dc16812cc 100644
--- a/sys/net/if_tun.h
+++ b/sys/net/if_tun.h
@@ -28,7 +28,6 @@ struct tun_softc {
 #define	TUN_DSTADDR	0x0010
 #define	TUN_RWAIT	0x0040
 #define	TUN_ASYNC	0x0080
-#define	TUN_NBIO	0x0100
 
 #define TUN_READY       (TUN_OPEN | TUN_INITED)