how to change the index chosen in plan?

I have a query like this:
select a.* from a inner join b on a.aid=b.aid where a.col1=33 a.col2=44
and b.bid=8
postgresql selected the index on a.col1 then selected the index on
b.bid. But in my situation, I know that the query will be faster if it
chose the index on b.bid first since there are only a few rows with
value 8. So I re-wrote the query as below:
select a.* from a where a.aid in (select aid from b where bid=8) and
a.col1=33 a.col2=44
But surprisingly, postgresql didn't change the plan. it still chose to
index scan on a.col1. How can I re-wirte the query so postgresql will
scan on b.bid first?