diff --git a/sbin/mount_unionfs/mount_unionfs.8 b/sbin/mount_unionfs/mount_unionfs.8
index 2a41aa6d3a0..4232a44f4e2 100644
--- a/sbin/mount_unionfs/mount_unionfs.8
+++ b/sbin/mount_unionfs/mount_unionfs.8
@@ -87,6 +87,10 @@ Hide the lower layer completely in the same way as mounting with
 To enforce file system security, the user mounting the file system
 must be superuser or else have write permission on the mounted-on
 directory.
+In addition, the
+.Em vfs.usermount
+.Xr sysctl 3
+variable must be set to 1 to permit file system mounting by ordinary users.
 .Pp
 Filenames are looked up in the upper layer and then in the
 lower layer.