Windowing functions vs aggregates

Cast of aggregate's type works:
# select avg(s)::int4 from foo;

but that doesn't work for with new windowing functions interface:
# select avg(s)::int4 OVER () from foo;
ERROR:  syntax error at or near "OVER"
LINE 1: select avg(s)::int4 OVER () from foo;

Is that intentional?

-- 
Teodor Sigaev                                   E-mail: teodor@sigaev.ru                                                   WWW: http://www.sigaev.ru/