Index: usr.sbin/autofs/automount.c
===================================================================
--- usr.sbin/autofs/automount.c
+++ usr.sbin/autofs/automount.c
@@ -84,6 +84,30 @@
 	return (error);
 }
 
+static int
+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);
+	else
+		f = auto_popen("umount", fsid, NULL);
+
+	assert(f != NULL);
+	return (auto_pclose(f));
+}
+
 static const struct statfs *
 find_statfs(const struct statfs *mntbuf, int nitems, const char *mountpoint)
 {
@@ -304,7 +328,8 @@
 			continue;
 		}
 
-		unmount_by_statfs(&(mntbuf[i]), force);
+		if (unmount_by_umount(&(mntbuf[i]), force) != 0)
+			unmount_by_statfs(&(mntbuf[i]), force);
 	}
 }