Postgres 9 alpha 5 revised, stored proc

I have this stored proc that works in pg 8.4.

create or replace function roundts(ts timestamp) returns timestamp as $$
declare
tmp integer;
result timestamp;
offset interval;
begin
tmp := extract(second from ts);
if tmp > 30 then
tmp := 60 - tmp;
offset := tmp || ' seconds';
result := ts + offset;
else
offset := tmp || ' seconds';
result := ts - offset;
end if;

tmp := extract(minute from result);
if tmp > 30 then
tmp := 60 - tmp;
offset := tmp || ' minutes';
result := result + offset;
else
offset := tmp || ' minutes';
result := result - offset;
end if;

return result;
end; $$ language plpgsql;

In 9 I get an error when trying to create it:

$ psql < roundts.sql
Timing is on.
CREATE FUNCTION
Time: 26.716 ms
ERROR: syntax error at or near "offset"
LINE 11: result := ts + offset;
^

Just wanted to report it.

-Andy