suspicious pointer/integer coersion

I have just noticed this code in plperl.c:
       hv_store(plperl_proc_hash, internal_proname, proname_len,                newSViv((IV) prodesc), 0);

basically, here prodesc is a pointer to a struct, and we are storing it 
as an integer in a perl hash for easy lookup by stringified oid.

How safe is this conversion on 64 bit platforms?

cheers

andrew