diff --git a/man2/mount_setattr.2 b/man2/mount_setattr.2
index 6ffe5e009..aa893f8c0 100644
--- a/man2/mount_setattr.2
+++ b/man2/mount_setattr.2
@@ -502,7 +502,7 @@ The underlying filesystem does not support ID-mapped mounts.
 .TP
 .B EINVAL
 The mount that is to be ID mapped is not a detached mount;
-that is, the mount is already visible in the filesystem.
+that is, the mount has not previously been visible in a mount namespace.
 .TP
 .B EINVAL
 A partial access-time setting was specified in
@@ -652,7 +652,11 @@ it must have been created by calling
 .BR open_tree (2)
 with the
 .B OPEN_TREE_CLONE
-flag and it must not already have been visible in the filesystem.
+flag and it must not already have been visible in a mount namespace.
+(To put things another way:
+the mount must not have been attached to the filesystem hierarchy
+with a system call such as
+.BR move_mount (2).)
 .PP
 ID mappings can be created for user IDs, group IDs, and project IDs.
 An ID mapping is essentially a mapping of a range of user or group IDs into