What is the best way to modify my query so that I also get the full name of the receiver in addition to the sender?

Thanks!

select u.uID
, concat (u.firstname, ' ', u.lastName) as sender
, m.senderID
, m.receiverID
, m.senderMessage
from users u
inner join messages m
on u.uID = m.senderID
where u.uID = m.receiverID or u.uID = m.senderID;