go ignores async code in letfn body

The following snippet fails because <! is outside of go boundaries.

(let [port (a/chan)]
  (a/go
    (letfn [(my-even? [n] (if (zero? n) true (my-odd? (dec n))))
            (my-odd? [n] (if (zero? n) false (my-even? (dec n))))]
      (my-even? (a/<! port)))))

Async code in letfn body should be rewritten by the go macro, given all bound functions can be properly initialized when the body starts.