diff --git a/src/net/cgrand/xforms.clj b/src/net/cgrand/xforms.clj
index 3902125..a4c9335 100644
--- a/src/net/cgrand/xforms.clj
+++ b/src/net/cgrand/xforms.clj
@@ -26,7 +26,12 @@
          ([~acc] (~rf ~acc))
          ([~acc ~binding] ~body)))))
 
-(defprotocol KvRf "Marker protocol for reducing fns that takes key and val as separate arguments.")
+(defprotocol KvRfable "Protocol for reducing fns that takes key and val as separate arguments."
+  (some-kvrf [f] "Returns a kvrf or nil"))
+
+(extend-protocol KvRfable
+  Object (some-kvrf [_] nil)
+  nil (some-kvrf [_] nil))
 
 (defmacro kvrf [name? & fn-bodies]
   (let [name (if (symbol? name?) name? (gensym '_))
@@ -34,7 +39,8 @@
         fn-bodies (if (vector? (first fn-bodies)) (list fn-bodies) fn-bodies)]
     `(reify
        clojure.lang.Fn
-       KvRf
+       KvRfable
+       (some-kvrf [this#] this#)
        clojure.lang.IFn
        ~@(clj/for [[args & body] fn-bodies]
            `(invoke [~name ~@args] ~@body)))))
@@ -45,7 +51,7 @@
   ([f]
     (fn [rf]
       (let [vacc (volatile! (f))]
-        (if (satisfies? KvRf f)
+        (if-some [f (some-kvrf f)]
           (kvrf
             ([] (rf))
             ([acc] (rf (rf acc (f (unreduced @vacc)))))
@@ -131,12 +137,10 @@
   ([kfn vfn xform] (by-key kfn vfn vector xform))
   ([kfn vfn pair xform]
     (fn [rf]
-      (let [make-rf (cond
-                      (and (= vector pair) (satisfies? KvRf rf))
-                      (fn [k] (fn ([acc] acc) ([acc v] (rf acc k v))))
-                      pair
-                      (fn [k] (fn ([acc] acc) ([acc v] (rf acc (pair k v)))))
-                      :else
+      (let [make-rf (if pair
+                      (if-some [rf (when (identical? vector pair) (some-kvrf rf))]
+                        (fn [k] (fn ([acc] acc) ([acc v] (rf acc k v))))
+                        (fn [k] (fn ([acc] acc) ([acc v] (rf acc (pair k v))))))
                       (constantly (multiplexable rf)))
             m (volatile! (transient {}))]
         (if (and (= key' kfn) (= val' vfn))