Problem with protocol implementation...

bug.clj

(ns rpg.bug
    (:require clojure.contrib.math))

(defprotocol CPARTS
  (real [c])
  (imag [c])
  (modulus [c])
  (phase [c]))

(defrecord complex [real imag]
  CPARTS
  (real [c] (:real c))
  (imag [c] (:imag c))
  (modulus [c]
    (clojure.contrib.math/sqrt
     (+ (* (real c) (real c)) (* (imag c) (imag c)))))
  (phase [c]
    (Math/atan (/ (imag c) (real c)))))

(defn mod2 [c]
  (clojure.contrib.math/sqrt
   (+ (* (real c) (real c)) (* (imag c) (imag c)))))

;;; works:
;;; (mod2 (complex. 1 1))
;;; crashes:
;;; (modulus (complex. 1 1))