SELECT INTO returning more than one row

Hi.

I have this problem in a plpgsql function:

SELECT INTO myvar col FROM table WHERE ...;

IF <query returns more than one row> THEN
do something
ELSE IF <query returns no rows> THEN
do something else
ELSE
do other things

If <query returns no rows> I know that myvar IS NULL OR GET DIAGNOSTICS
ROW_COUNT is zero.

Is there a way to know if the query returned more than one row?
In Oracle PL/SQL I can catch the TOO_MANY_ROWS exception but in Postgres
I found no way for doing it:

- myvar is correctly valued with the first occurrence of the result
- FOUND is TRUE
- GET DIAGNOSTICS ROW_COUNT is 1 (it counts only fetched rows)

I tried to use a cursor but the only way to know how many rows it
returned is to fetch them all. (And I don't like this solution)

Thanks in advance.