diff --git a/src/taoensso/sente/packers/transit.cljx b/src/taoensso/sente/packers/transit.cljx
index 289427b..87f2332 100644
--- a/src/taoensso/sente/packers/transit.cljx
+++ b/src/taoensso/sente/packers/transit.cljx
@@ -22,46 +22,86 @@
    [cognitect.transit :as transit]
    [taoensso.sente.interfaces :as interfaces :refer (pack unpack)]))
 
-;;;; TODO
-;; * Note that Transit-cljs doesn't seem to actually have msgpack support atm?
-;; * Invesigate the actual cost of cljs+clj side writer/reader construction -
-;;   is it worth caching these?
-;; * Is it worth considering a cljs-side baos/bais pool?
-
+#+clj
 (defn- get-charset [transit-fmt]
   ;; :msgpack appears to need ISO-8859-1 to retain binary data correctly when
   ;; string-encoded, all other (non-binary) formats can get UTF-8:
   (if (enc/kw-identical? transit-fmt :msgpack) "ISO-8859-1" "UTF-8"))
 
-(def ^:private -transit-writer
-  #+cljs (encore/memoize_ (fn [     fmt opts] (transit/writer      fmt opts)))
-  #+clj                   (fn [baos fmt opts] (transit/writer baos fmt opts)))
+#+clj
+(def ^:private cache-read-handlers
+  "reader-opts -> reader-opts with cached read handler map"
+  (let [cache (enc/memoize_ (fn [m] (transit/read-handler-map m)))]
+    (fn [reader-opts]
+      (if-let [m (:handlers reader-opts)]
+        (assoc reader-opts :handlers (cache m))
+        reader-opts))))
+
+#+clj
+(def ^:private cache-write-handlers
+  "writer-opts -> writer-opts with cached write handler map"
+  (let [cache (enc/memoize_ (fn [m] (transit/write-handler-map m)))]
+    (fn [writer-opts]
+      (if-let [m (:handlers writer-opts)]
+        (assoc writer-opts :handlers (cache m))
+        writer-opts))))
+
+#+clj
+(def ^:private transit-writer-fn-proxy
+  (enc/thread-local-proxy
+    (fn [fmt opts]
+      (let [^String charset (get-charset fmt)
+            opts (cache-write-handlers opts)
+            ^ByteArrayOutputStream baos (ByteArrayOutputStream. 512)
+            writer (transit/writer baos fmt opts)]
+        (fn [x]
+          (transit/write writer x)
+          (let [result (.toString baos charset)]
+            (.reset baos)
+            result))))))
 
-(def ^:private -transit-reader
-  #+cljs (encore/memoize_ (fn [     fmt opts] (transit/reader      fmt opts)))
-  #+clj                   (fn [bais fmt opts] (transit/reader bais fmt opts)))
+(def ^:private get-transit-writer-fn
+  "Returns thread-safe (fn [x-to-write])"
+  #+cljs
+  (enc/memoize_
+    (fn [fmt opts]
+      (let [writer (transit/writer fmt opts)]
+        (fn [x] (transit/write writer x)))))
+
+  #+clj
+  (fn [fmt opts]
+    (let [thread-local-transit-writer-fn (.get ^ThreadLocal transit-writer-fn-proxy)]
+      (thread-local-transit-writer-fn fmt opts))))
+
+(def ^:private get-transit-reader-fn
+  "Returns thread-safe (fn [str-to-read])"
+  #+cljs
+  (enc/memoize_
+    (fn [fmt opts]
+      (let [reader (transit/reader fmt opts)]
+        (fn [s] (transit/read reader s)))))
+
+  #+clj
+  (fn [fmt opts]
+    (let [^String charset (get-charset fmt)
+          opts (cache-read-handlers opts)]
+      (fn [s]
+        (let [ba (.getBytes ^String s ^String charset)
+              ^ByteArrayInputStream bais (ByteArrayInputStream. ba)
+              reader (transit/reader bais fmt opts)]
+          (transit/read reader))))))
 
 (deftype TransitPacker [transit-fmt writer-opts reader-opts]
   taoensso.sente.interfaces/IPacker
-  (pack [_ x]
-    #+cljs (transit/write (-transit-writer transit-fmt writer-opts) x)
-    #+clj  (let [charset (get-charset transit-fmt)
-                 ^ByteArrayOutputStream baos (ByteArrayOutputStream. 512)]
-             (transit/write (-transit-writer baos transit-fmt writer-opts) x)
-             (.toString baos ^String charset)))
-
-  (unpack [_ s]
-    #+cljs (transit/read (-transit-reader transit-fmt reader-opts) s)
-    #+clj  (let [charset (get-charset transit-fmt)
-                 ba (.getBytes ^String s ^String charset)
-                 ^ByteArrayInputStream bais (ByteArrayInputStream. ba)]
-             (transit/read (-transit-reader bais transit-fmt reader-opts)))))
+  (pack   [_ x] ((get-transit-writer-fn transit-fmt writer-opts) x))
+  (unpack [_ s] ((get-transit-reader-fn transit-fmt reader-opts) s)))
 
 (defn get-transit-packer "Returns a new TransitPacker"
   ([           ] (get-transit-packer :json       {} {}))
   ([transit-fmt] (get-transit-packer transit-fmt {} {}))
   ([transit-fmt writer-opts reader-opts]
-   (have? [:el #{:json :msgpack}] transit-fmt)
+   ;; No transit-cljs support for msgpack atm
+   (have? [:el #{:json #_:msgpack}] transit-fmt)
    (have? map? writer-opts reader-opts)
    (TransitPacker. transit-fmt writer-opts reader-opts)))