[plt-scheme] Callbacks returning void

I see that something like this has been asked once before [1], but
there didn't seem to be an answer so I'll ask it. I've bound a
function as follows:

(dSpaceCollide _dSpaceID _pointer (_fun _pointer _dGeomID _dGeomID ->
_void) -> _void)

When I pass it a scheme function as the third argument, I get the
following error message when it (the callback) returns:

Scheme->C: expects argument of type <non-void-C-type>; given #<ctype>

Is this supposed to work?

    Henk

[1] http://www.cs.brown.edu/pipermail/plt-scheme/2007-July/019775.html