diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c
index 23af5ba66c2a..271b506c335a 100644
--- a/sys/kern/kern_descrip.c
+++ b/sys/kern/kern_descrip.c
@@ -2102,6 +2102,7 @@ fdsetugidsafety(struct thread *td)
 
 	fdp = td->td_proc->p_fd;
 	KASSERT(fdp->fd_refcnt == 1, ("the fdtable should not be shared"));
+	MPASS(fdp->fd_nfiles >= 3);
 	for (i = 0; i <= 2; i++) {
 		fp = fdp->fd_ofiles[i].fde_file;
 		if (fp != NULL && is_unsafe(fp)) {