diff --git a/README.md b/README.md
index f43d5201..6b444325 100644
--- a/README.md
+++ b/README.md
@@ -262,6 +262,10 @@ and has access to the full application state. Try and keep the logic in these
 bulk of your logic will safely shielded, with only a few points touching every
 part of your application.
 
+Within the scope of `reducers` and `effects`, you can access the current `state`,
+however, the object is frozen, disallowing changes. To update the state, you 
+must return an object with your updates from a `reducer`.
+
 ## Effects
 Side effects are done through `effects` declared in `app.model()`. Unlike
 `reducers` they cannot modify the state by returning objects, but get a
diff --git a/index.js b/index.js
index 473f81ed..7a146846 100644
--- a/index.js
+++ b/index.js
@@ -139,19 +139,19 @@ function choo () {
       const _reducers = ns ? reducers[ns] : reducers
       if (_reducers && _reducers[action.type]) {
         if (ns) {
-          const reducedState = _reducers[action.type](action, state[ns])
+          const reducedState = _reducers[action.type](action, Object.freeze(state[ns]))
           if (!newState[ns]) newState[ns] = {}
           mutate(newState[ns], xtend(state[ns], reducedState))
         } else {
-          mutate(newState, reducers[action.type](action, state))
+          mutate(newState, reducers[action.type](action, Object.freeze(state)))
         }
         reducersCalled = true
       }
 
       const _effects = ns ? effects[ns] : effects
       if (_effects && _effects[action.type]) {
-        if (ns) _effects[action.type](action, state[ns], send)
-        else _effects[action.type](action, state, send)
+        if (ns) _effects[action.type](action, Object.freeze(state[ns]), send)
+        else _effects[action.type](action, Object.freeze(state), send)
         effectsCalled = true
       }
 
diff --git a/tests/z-disabled-browser.js b/tests/z-disabled-browser.js
new file mode 100644
index 00000000..26792ee7
--- /dev/null
+++ b/tests/z-disabled-browser.js
@@ -0,0 +1,55 @@
+const tape = require('tape')
+const choo = require('../')
+
+tape('should render on the client', {skip: true}, function (t) {
+  t.test('state should not be mutable', function (t) {
+    t.plan(3)
+
+    const app = choo()
+    const state = {
+      foo: 'baz',
+      beep: 'boop'
+    }
+    app.model({
+      state: state,
+      reducers: {
+        mutate: (action, state) => {
+          state.foo = 'zap'
+          return {}
+        },
+        noMutate: (action, state) => {
+          return {beep: 'poob'}
+        }
+      },
+      effects: {
+        effectMutate: (action, state) => {
+          state.foo = 'zap'
+        }
+      }
+    })
+
+    app.router((route) => [
+      route('/', function (params, state, send) {
+        const okd = (evt) => {
+          if (evt.key === 'a') {
+            send('mutate')
+          } else {
+            send('noMutate')
+          }
+        }
+        return choo.view`<span class="test" onkeydown=${okd}>${state.foo}:${state.beep}</span>`
+      })
+    ])
+    document.body.appendChild(app.start())
+    const $el = document.querySelector('.test')
+    const mutate = new window.KeyboardEvent('keydown', {key: 'a'})
+    const noMutate = new window.KeyboardEvent('keydown', {key: 'b'})
+    const effectMutate = new window.KeyboardEvent('keydown', {key: 'c'})
+    $el.dispatchEvent(mutate)
+    t.equal($el.innerText, 'baz:boop', 'state did not mutate')
+    $el.dispatchEvent(noMutate)
+    t.equal($el.innerText, 'baz:poob', 'state was updated from a return')
+    $el.dispatchEvent(effectMutate)
+    t.equal($el.innerText, 'baz:poob', 'state was not updated from an effect')
+  })
+})