can't pass enum to function returning struct by value

[3b]

(cffi:defcenum enum
  (:foo 16))

(cffi:defcstruct foo
  (:foo :pointer))

 ;; not really valid function definitions, malloc is just first function i thought of.
;; error happens before the call though
(cffi:defcfun ("malloc" foo) (:struct foo)
  (foo enum))

(cffi:defcfun ("malloc" foo2) :pointer
  (foo enum))

(foo2 :foo)
;; -> #.(SB-SYS:INT-SAP #X006452E0)

(foo :foo)

debugger invoked on a TYPE-ERROR in thread
#<THREAD "main thread" RUNNING {1003A768B3}>:
  The value 16 is not of type SYSTEM-AREA-POINTER.

cffi 0.15, 64 bit sbcl on linux and windows