diff --git a/sys/kern/uipc_socket.c b/sys/kern/uipc_socket.c
--- a/sys/kern/uipc_socket.c
+++ b/sys/kern/uipc_socket.c
@@ -5044,6 +5044,7 @@
 	xso->so_uid = so->so_cred->cr_uid;
 	xso->so_pgid = so->so_sigio ? so->so_sigio->sio_pgid : 0;
 	SOCK_LOCK(so);
+	xso->so_fibnum = so->so_fibnum;
 	if (SOLISTENING(so)) {
 		xso->so_qlen = so->sol_qlen;
 		xso->so_incqlen = so->sol_incqlen;
diff --git a/sys/sys/socketvar.h b/sys/sys/socketvar.h
--- a/sys/sys/socketvar.h
+++ b/sys/sys/socketvar.h
@@ -615,7 +615,8 @@
 	uint32_t	so_qlimit;
 	pid_t		so_pgid;
 	uid_t		so_uid;
-	int32_t		so_spare32[8];
+	int		so_fibnum;
+	int32_t		so_spare32[7];
 	int16_t		so_type;
 	int16_t		so_options;
 	int16_t		so_linger;