Postgres plpgsql error when trying to create function

Postgres 9.5.2

Getting:

ERROR:  syntax error at end of input
LINE 14: ...ast_modified_at, NEW.first_name, NEW.last_name);

for these statements in a psql shell, right after running $$;:

CREATE OR REPLACE FUNCTION customer_history_trigger() RETURNS trigger
    LANGUAGE plpgsql SECURITY DEFINER
    AS $$
BEGIN
    NEW.last_modified_at = now();
    IF (TG_OP = 'UPDATE') THEN
        IF OLD.status IS DISTINCT FROM NEW.status or OLD.parent_id IS DISTINCT FROM NEW.parent_id
        or OLD.first_name IS DISTINCT FROM NEW.first_name or OLD.last_name IS DISTINCT FROM NEW.last_name
        or OLD.company IS DISTINCT FROM NEW.company or OLD.company_alias IS DISTINCT FROM NEW.company_alias
        THEN
            INSERT INTO customerhistory
                (customer_id, modified_at, first_name, last_name)
            VALUES
                (NEW.id, NEW.last_modified_at, NEW.first_name, NEW.last_name);
        END IF;
    ELSIF (TG_OP = 'INSERT') THEN
        INSERT INTO customerhistory
            (customer_id, modified_at, first_name, last_name)
        VALUES
            (NEW.id, NEW.last_modified_at, NEW.first_name, NEW.last_name);
    END IF;
    RETURN NEW;
END;
$$;

There's also a little arrow in the error pointing to the semicolon at the end of the line. So clearly, it doesn't like the semi colon at the end of this line: (NEW.id, NEW.last_modified_at, NEW.first_name, NEW.last_name); but I can't figure out why.