bug: select date 'infinity' gives error

According to the docs at 
http://www.postgresql.org/idocs/index.php?datatype-datetime.html, 
'infinity' is a valid date input. I quote:

"The following SQL-compatible functions can be used as date or time 
input ... 'infinity' [...]"

but I get the following error when trying to set a date to infinity ...

$ psql DB -c "select date 'infinity'"
ERROR:  Unrecognized date external representation 'infinity'

whereas it works as as a timestamp ...

$ psql DB -c "select timestamp 'infinity'"
  timestamptz
-------------
  infinity
(1 row)

Is my syntax wrong?