update recipient causing row level lock in postgresql

hello sir/madam, 

I'm having issue with update of recipient table.

the issue i'm having is that in order to update, campaign acquires row level lock using select ... for update statement.

however the issue is that there's 2 tables involves with the 'select for update' statement using join.

let me explain with an example. 

something like this will be executed prior to update.

select a....

  from tablea 

   join tableb

    on tablea.o = tableb=o

 where tableb.c = $1

    and tablea.d = $2

     for update;

the problem is that the value of $2 is different but $1 has same value which is causing row level lock in tableb.

I'm considering using custom query for the update job but having difficulty adapting it.

could anyone give me some advice ? 

thank you in advance.

regards,

sean