diff --git a/man2/umount.2 b/man2/umount.2
index bc826776e..dae0f7e42 100644
--- a/man2/umount.2
+++ b/man2/umount.2
@@ -141,6 +141,11 @@ points outside the user address space.
 is not a mount point.
 .TP
 .B EINVAL
+.I target
+is locked; see
+.BR mount_namespaces (7).
+.TP
+.B EINVAL
 .BR umount2 ()
 was called with
 .B MNT_EXPIRE