Can you show me how to return a double from the FFI?

Simple example, C header is like this: 

double add_doubles ( double x, double y );

So i try to do this:

(ct:defun-dll add_doubles ((x :double) (y :double))
 :return-type :double
 :library-name *cmt-library*
 :entry-name "add_doubles") 

The compiler says "cant return type double"

Can you show me a simple example of a defun-dll
for this example? [A long time ago I had this working
on PROCYON CL but it was necessary to fake out the
C program so that the assembler allocated an extra
double on the stack. Damned if I can remember the
details... so please show me the "right" way to do this.]

---------------------------------------------------
Name: Martin Mallinson
E-mail: <cmt.com at martin.mallinson> (Martin Mallinson)
Date: 6/10/97
Time: 8:14:19 AM
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