PL/SQL :: Single Sub Row Query Returns More Than 1 Row?

I am trying to update values in a table from another table and getting the error: Single Sub Row Query Returns More Than 1 Row.

I want table B's PRV_NAME updated into table A's PRV_NAME where A.PRVID = B.PRVID where B.PRV_TYPE = M'

Both tables have all unique PRVID's, however, table B has PRVID's that have the same name. So table B data can look like this:

PRVID PRV_NAME
1234 PHOENIX MED
1235 SAC MED
1236 SAC MED
1237 OVERLAND
etc..

So, as you can see the PRVID's are unique, but not the PRV_NAME's. Is this the reason why I get this error?

I did not build the tables and have no control over what is put in them. If this is the reason for the error, is there any way to resolve this?

For reference, here is the query.

update msb_prv_source ps
set ps.prv_name =
(select prv00.prv00_prv_name
from prv00_prv prv00
join msb_prv_source ps
on prv00.prv00_prv_id = ps.prvid
where prv00.prv00_prv_type = 'M')