diff --git a/src/React.js b/src/React.js
index 2d42dd1..6833ab4 100644
--- a/src/React.js
+++ b/src/React.js
@@ -53,6 +53,17 @@ function readState(this_) {
 }
 exports.readState = readState;
 
+function transformState(this_){
+  return function(update){
+    return function(){
+      this_.setState(function(old, props){
+        return {state: update(old.state)};
+      });
+    };
+  };
+}
+exports.transformState = transformState;
+
 function createClass(spec) {
   var result = {
     displayName: spec.displayName,
diff --git a/src/React.purs b/src/React.purs
index a5c63fb..15541ab 100644
--- a/src/React.purs
+++ b/src/React.purs
@@ -284,10 +284,7 @@ foreign import writeState :: forall props state access eff. ReactThis props stat
 foreign import readState :: forall props state access eff. ReactThis props state -> Eff (state :: ReactState (read :: Read | access) | eff) state
 
 -- | Transform the component state by applying a function.
-transformState :: forall props state eff. ReactThis props state -> (state -> state) -> Eff (state :: ReactState ReadWrite | eff) state
-transformState ctx f = do
-  state <- readState ctx
-  writeState ctx $ f state
+foreign import transformState :: forall props state eff. ReactThis props state -> (state -> state) -> Eff (state :: ReactState ReadWrite | eff) Unit
 
 -- | Create a React class from a specification.
 foreign import createClass :: forall props state eff. ReactSpec props state eff -> ReactClass props