SQL & PL/SQL

I have a piece of SQL similar to:

SELECT person,
amount,
type,
SUM(amount) OVER (PARTITION BY person) sum_amount_person
FROM table_a

What I would like to be able to do is use a conditional PARTITION BY clause, so rather than partition and summing for each person I would like to be able to sum for each person where type = 'ABC'

I would expect the syntax to be something like

SELECT person,
amount,
type,
SUM(amount) OVER (PARTITION BY person WHERE type = 'ABC') sum_amount_person
FROM table_a

Is this possible? Or am I missing a much simpler solution?

Richard