diff --git a/index.js b/index.js
index 464c709..c9044bd 100644
--- a/index.js
+++ b/index.js
@@ -45,6 +45,14 @@ module.exports = function(opts, app){
     throw new TypeError('app instance required: `session(opts, app)`');
   }
 
+  // setup encoding/decoding
+  if (!(typeof opts.encode === 'function')) {
+    opts.encode = encode
+  }
+  if (!(typeof opts.decode === 'function')) {
+    opts.decode = decode
+  }
+
   // to pass to Session()
   app.context.sessionKey = opts.key;
 
@@ -63,7 +71,7 @@ module.exports = function(opts, app){
       try {
         // make sure sessionOptions exists
         initSessionOptions(this, opts);
-        var obj = decode(json);
+        var obj = opts.decode(json);
         if (typeof opts.valid === 'function' && !opts.valid(this, obj)) {
           // valid session value fail, ignore this session
           sess = new Session(this);
@@ -72,7 +80,7 @@ module.exports = function(opts, app){
         } else {
           sess = new Session(this, obj);
           // make prev a different object from sess
-          json = decode(json);
+          json = opts.decode(json);
         }
       } catch (err) {
         // backwards compatibility:
@@ -278,9 +286,14 @@ Session.prototype.save = function(){
   json._expire = maxAge + Date.now();
   json._maxAge = maxAge;
 
-  json = encode(json);
-  debug('save %s', json);
-  ctx.cookies.set(key, json, opts);
+  try {
+    json = opts.encode(json);
+    debug('save %s', json);
+    ctx.cookies.set(key, json, opts);
+  } catch (e) {
+    debug('encode %j error: %s', json, err);
+    ctx.cookies.set(key, '', opts);
+  }
 };
 
 /**
diff --git a/test/test.js b/test/test.js
index e7d4900..4290409 100644
--- a/test/test.js
+++ b/test/test.js
@@ -527,6 +527,55 @@ describe('Koa Session', function(){
       });
     })
   })
+
+  describe('when options.encode and options.decode are functions', function () {
+    describe('they are used to encode/decode stored cookie values', function () {
+      it('should work', function (done) {
+        var encodeCallCount = 0
+        var decodeCallCount = 0
+
+        function encode(data) {
+          ++encodeCallCount
+          return JSON.stringify({enveloped: data})
+        }
+        function decode(data) {
+          ++decodeCallCount
+          return JSON.parse(data).enveloped
+        }
+
+        var app = koa();
+        app.keys = ['a', 'b'];
+        app.use(session({
+          encode: encode,
+          decode: decode
+        }, app));
+
+        app.use(function * () {
+          this.session.counter = (this.session.counter || 0) + 1
+          this.body = this.session
+          return
+        })
+
+        request(app.callback())
+          .get('/')
+          .expect(function () { encodeCallCount.should.above(0, 'encode was not called'); })
+          .expect(200, function (err, res) {
+            should.not.exist(err)
+            res.body.counter.should.equal(1, 'expected body to be equal to session.counter')
+            var cookies = res.headers['set-cookie'].join(';');
+            request(app.callback())
+              .get('/')
+              .set('Cookie', cookies)
+              .expect(function () { decodeCallCount.should.be.above(1, 'decode was not called'); })
+              .expect(200, function (err, res) {
+                should.not.exist(err);
+                res.body.counter.should.equal(2);
+                done();
+              })
+          })
+      })
+    })
+  })
 })
 
 function App(options) {