Index: usr.sbin/autofs/automount.c
===================================================================
--- usr.sbin/autofs/automount.c
+++ usr.sbin/autofs/automount.c
@@ -88,21 +88,14 @@
 unmount_by_umount(struct statfs* sfp, bool force)
 {
 	FILE *f;
-	char fsid[sizeof(sfp->f_fsid)*2+1];
-	size_t i;
 
 	if (sfp->f_fsid.val[0] == 0 || sfp->f_fsid.val[1] == 0)
 		return (-1);
 
-	/* umount(8) expects the file system ID to be in hexadecimal format */
-	for (i = 0; i < sizeof(sfp->f_fsid); i++)
-		snprintf(fsid+strlen(fsid), sizeof(fsid) - strlen(fsid),
-		    "%02x", ((u_char *)&sfp->f_fsid)[i]);
-
 	if (force)
-		f = auto_popen("umount", "-f", fsid, NULL);
+		f = auto_popen("umount", "-f", sfp->f_mntfromname, NULL);
 	else
-		f = auto_popen("umount", fsid, NULL);
+		f = auto_popen("umount", sfp->f_mntfromname, NULL);
 
 	assert(f != NULL);
 	return (auto_pclose(f));