timestamp() broken in 7.2.4?

In 7.1.3 I can use

select timestamp(date '2001-01-01', time '00:00');

but in 7.2.4 I get

db1=# select timestamp(date '2001-01-01', time '00:00');
ERROR: parser: parse error at or near "date"

I get the same error when using actual columns in actual tables. Both
PostgreSQL versions are compiled from source on a Intel Linux box.

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