postgresql 9.6 alter column type which used in function

gistfile1.txt

create table my_table (id integer primary key, data text);
create function my_func(id integer, data text) 
returns void
language plpgsql
as 
$$
begin
insert into my_table values (id, data);
end;
$$;

select my_func (10, 'asdf');
alter table my_table alter column id type bigint;

\d my_table