Hello, Apparently SIZE is not evaluated at macro expansion time. I basically want to pass the name of a foreign function as SIZE and have it evaluated. What would be the best way to do that? Currently I'm doing this: (eval-when (:compile-toplevel :load-toplevel :execute) (cffi:define-foreign-library libfoo (:unix "libfoo.so")) (cffi:load-foreign-library 'libfoo) (cffi:defctype size :uint) (cffi:defcfun ("foo_size" foo-size) size)) (macrolet ((m () `(cffi:defcstruct (foo-struct :size ,(eval-when (:compile-toplevel :load-toplevel :execute) (foo-size))) (data :pointer)))) (m))