pg_get_functiondef and overloaded functions

Hi,

I'm playing around with the new pg_get_functiondef() function but I can't get it to work when I need to specify the
argumentlist. 
 

select pg_get_functiondef('foo'::regproc)

works without problems. 

However if I have e.g. foo(int) and foo(int, int) I can't get this to work. 

I tried 

select pg_get_functiondef('foo(int)'::regproc)
select pg_get_functiondef('foo(int4)'::regproc)
select pg_get_functiondef('foo(integer)'::regproc)

but each time I get the error: function "foo(integer)" does not exist  

What am I missing?

Regards
Thomas