--- b/usr.sbin/autofs/automount.c	
+++ b/usr.sbin/autofs/automount.c	
@@ -63,24 +63,64 @@ __FBSDID("$FreeBSD$");
 static int
 unmount_by_statfs(const struct statfs *sb, bool force)
 {
+	int error;
+
+	if ((error = unmount_automount(&sb->f_fsid, force ? MNT_FORCE : 0)) != 0)
+		log_warn("cannot unmount %s (FSID:%d:%d)",
+		    sb->f_mntonname, sb->f_fsid.val[0], sb->f_fsid.val[1]);
+
+	return (error);
+}
+
+
+static int
+unmount_by_umount(const fsid_t *fsid, int flags)
+{
+	FILE *f;
+	char fsid_str[sizeof(*fsid)*2+1];
+	size_t i;
+
+	/* umount(8) expects the file system ID to be in hexadecimal format */
+	for (i = 0; i < sizeof(*fsid); i++)
+		snprintf(fsid_str+(i*2), sizeof(fsid_str) - (i*2),
+		    "%02x", ((const u_char *)fsid)[i]);
+
+	if (flags & MNT_FORCE)
+		f = auto_popen("umount", "-f", fsid_str, NULL);
+	else
+		f = auto_popen("umount", fsid_str, NULL);
+
+	assert(f != NULL);
+	return (auto_pclose(f));
+}
+
+/*
+ * Unmount a filesystem. Default to umount(8) and fallback to unmount(3).
+ */
+int
+unmount_automount(const fsid_t *fsid, int flags)
+{
+	int error;
 	char *fsid_str;
-	int error, ret, flags;
 
-	ret = asprintf(&fsid_str, "FSID:%d:%d",
-	    sb->f_fsid.val[0], sb->f_fsid.val[1]);
-	if (ret < 0)
+	/* need to find reference where FSID:0:0 is error */
+	if (fsid->val[0] == 0 || fsid->val[1] == 0)
+		return (EACCES);
+
+	/* any debug or warnings will be logged from auto_pclose() */
+	if ((error = unmount_by_umount(fsid, flags)) == 0)
+		return (0);
+
+	if (asprintf(&fsid_str, "FSID:%d:%d", fsid->val[0], fsid->val[1]) < 0)
 		log_err(1, "asprintf");
 
-	log_debugx("unmounting %s using %s", sb->f_mntonname, fsid_str);
+	flags |= MNT_BYFSID;
+	if ((error = unmount(fsid_str, flags)) == 0)
+		return (0);
 
-	flags = MNT_BYFSID;
-	if (force)
-		flags |= MNT_FORCE;
-	error = unmount(fsid_str, flags);
-	free(fsid_str);
-	if (error != 0)
-		log_warn("cannot unmount %s", sb->f_mntonname);
+	log_debugx("cannot unmount (%s): %s", fsid_str, strerror(errno));
 
+	free(fsid_str);
 	return (error);
 }
 
--- b/usr.sbin/autofs/autounmountd.c	
+++ b/usr.sbin/autofs/autounmountd.c	
@@ -154,25 +154,11 @@ refresh_automounted(void)
 static int
 unmount_by_fsid(const fsid_t fsid, const char *mountpoint)
 {
-	char *fsid_str;
-	int error, ret;
-
-	ret = asprintf(&fsid_str, "FSID:%d:%d", fsid.val[0], fsid.val[1]);
-	if (ret < 0)
-		log_err(1, "asprintf");
-
-	error = unmount(fsid_str, MNT_NONBUSY | MNT_BYFSID);
-	if (error != 0) {
-		if (errno == EBUSY) {
-			log_debugx("cannot unmount %s (%s): %s",
-			    mountpoint, fsid_str, strerror(errno));
-		} else {
-			log_warn("cannot unmount %s (%s)",
-			    mountpoint, fsid_str);
-		}
-	}
+	int error;
 
-	free(fsid_str);
+	if ((error = unmount_automount(&fsid, MNT_NONBUSY)) != 0)
+		log_warn("cannot unmount %s (FSID:%d:%d)",
+		    mountpoint, fsid.val[0], fsid.val[1]);
 
 	return (error);
 }
--- b/usr.sbin/autofs/common.h	
+++ b/usr.sbin/autofs/common.h	
@@ -33,6 +33,7 @@ 
 #ifndef AUTOMOUNTD_H
 #define	AUTOMOUNTD_H
 
+#include <sys/mount.h>
 #include <sys/queue.h>
 #include <stdbool.h>
 
@@ -104,6 +105,8 @@ int	main_autounmountd(int argc, char **argv);
 FILE	*auto_popen(const char *argv0, ...);
 int	auto_pclose(FILE *iop);
 
+int unmount_automount(const fsid_t *fsid, int flags);
+
 /*
  * lex(1) stuff.
  */