Help with prepared statement

Hello,
I am having some difficulty using a prepared statement.

PREPARE fooplan(int4, int4) AS SELECT * FROM records WHERE id = $1
AND fax = $2;

Normally this works fine like this:
EXECUTE fooplan(42985, 12345678);

However, sometimes I need to match NULL values like this:

EXECUTE fooplan(42985, NULL);

This fails of course since "fax = NULL" is not the same as "fax IS
NULL".

Is there any way around this?

Thanks!