cast affects use of indexes ?

Guys,

I've got a table with an indexed column of a numeric user
type (implemented in C). When I run a select on that table
in a form of :

select * from sometable where column = 89464;

sequential scan is used...

When I rewrite the query to use cast like this :

select * from sometable where column = 89464::mytype;

bitmap index scan and bitmap heap scan are used.

Is it possible to make it work properly without
use of explicit casts ? Thanks!

Best regards,
Alex Vinogradovs