diff --git a/src/main/java/com/github/nkzawa/socketio/client/Socket.java b/src/main/java/com/github/nkzawa/socketio/client/Socket.java
index 9ea09ac..f2b4390 100644
--- a/src/main/java/com/github/nkzawa/socketio/client/Socket.java
+++ b/src/main/java/com/github/nkzawa/socketio/client/Socket.java
@@ -5,9 +5,8 @@ import com.github.nkzawa.socketio.parser.Packet;
 import com.github.nkzawa.socketio.parser.Parser;
 import com.google.gson.Gson;
 import com.google.gson.JsonArray;
-import com.google.gson.reflect.TypeToken;
+import com.google.gson.JsonElement;
 
-import java.lang.reflect.Type;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentLinkedQueue;
@@ -82,11 +81,11 @@ public class Socket extends Emitter {
             LinkedList<Object> _args = new LinkedList<Object>(Arrays.asList(args));
             if (_args.peekLast() instanceof Ack) {
                 Ack ack = (Ack)_args.pollLast();
-                return this.emit(event, ack, _args.toArray());
+                return this.emit(event, _args.toArray(), ack);
             }
 
             _args.offerFirst(event);
-            Packet packet = new Packet(Parser.EVENT, gson.toJsonTree(_args.toArray()));
+            Packet packet = new Packet(Parser.EVENT, toJsonArray(_args));
             this.packet(packet);
         }
 
@@ -94,19 +93,19 @@ public class Socket extends Emitter {
     }
 
     /**
-     * An alias method for `emit` with `ack`
+     * emit with an ack callback
      *
      * @param event
-     * @param ack
      * @param args
+     * @param ack
      * @return
      */
-    public Emitter emit(final String event, Ack ack, final Object... args) {
+    public Emitter emit(final String event, final Object[] args, Ack ack) {
         List<Object> _args = new ArrayList<Object>() {{
             add(event);
             addAll(Arrays.asList(args));
         }};
-        Packet packet = new Packet(Parser.EVENT, gson.toJsonTree(_args.toArray()));
+        Packet packet = new Packet(Parser.EVENT, toJsonArray(_args));
 
         int ids = this.ids.getAndIncrement();
         logger.info(String.format("emitting packet with ack id %d", ids));
@@ -138,14 +137,13 @@ public class Socket extends Emitter {
         this.subs.add(On.on(io, Manager.EVENT_PACKET, new Listener() {
             @Override
             public void call(Object... objects) {
-                Packet packet = objects.length > 0 ? (Packet)objects[0] : null;
-                Socket.this.onpacket(packet);
+                Socket.this.onpacket((Packet)objects[0]);
             }
         }));
         this.subs.add(On.on(io, Manager.EVENT_CLOSE, new Listener() {
             @Override
             public void call(Object... objects) {
-                String reason = objects.length > 0 ? (String)objects[0] : null;
+                String reason = objects.length > 0 ? (String) objects[0] : null;
                 Socket.this.onclose(reason);
             }
         }));
@@ -185,8 +183,7 @@ public class Socket extends Emitter {
     }
 
     private void onevent(Packet packet) {
-        Type type = new TypeToken<LinkedList<Object>>(){}.getType();
-        LinkedList<Object> args = gson.fromJson(packet.data != null ? packet.data : new JsonArray(), type);
+        LinkedList<Object> args = new LinkedList<Object>(fromJsonArray(packet.data.getAsJsonArray()));
         logger.info(String.format("emitting event %s", args));
 
         if (packet.id >= 0) {
@@ -221,7 +218,7 @@ public class Socket extends Emitter {
     private void onack(Packet packet) {
         logger.info(String.format("calling ack %s with %s", packet.id, packet.data));
         Ack fn = this.acks.remove(packet.id);
-        fn.call(gson.fromJson(packet.data, Object[].class));
+        fn.call(fromJsonArray(packet.data.getAsJsonArray()).toArray());
     }
 
     private void onconnect() {
@@ -273,6 +270,22 @@ public class Socket extends Emitter {
         return this.close();
     }
 
+    private static JsonArray toJsonArray(List<Object> list) {
+        JsonArray data = new JsonArray();
+        for (Object v : list) {
+            data.add(v instanceof JsonElement ? (JsonElement)v : gson.toJsonTree(v));
+        }
+        return data;
+    }
+
+    private static List<Object> fromJsonArray(JsonArray array) {
+        List<Object> data = new ArrayList<Object>();
+        for (JsonElement v : array) {
+            data.add(v.isJsonPrimitive() ? gson.fromJson(v, Object.class) : v);
+        }
+        return data;
+    }
+
 
     public static interface Ack {
 
diff --git a/src/test/java/com/github/nkzawa/socketio/client/IOTest.java b/src/test/java/com/github/nkzawa/socketio/client/IOTest.java
index be5da7d..7ed701c 100644
--- a/src/test/java/com/github/nkzawa/socketio/client/IOTest.java
+++ b/src/test/java/com/github/nkzawa/socketio/client/IOTest.java
@@ -1,6 +1,8 @@
 package com.github.nkzawa.socketio.client;
 
 import com.github.nkzawa.emitter.Emitter;
+import com.google.gson.Gson;
+import com.google.gson.JsonElement;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -11,6 +13,8 @@ import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.net.URISyntaxException;
+import java.util.HashMap;
+import java.util.Map;
 import java.util.concurrent.*;
 
 import static org.hamcrest.CoreMatchers.is;
@@ -110,7 +114,7 @@ public class IOTest {
 
     @Test(timeout = TIMEOUT)
     public void message() throws URISyntaxException, InterruptedException {
-        final BlockingQueue<String> events = new LinkedBlockingQueue<String>();
+        final BlockingQueue<Object[]> events = new LinkedBlockingQueue<Object[]>();
 
         IO.Options opts = new IO.Options();
         opts.forceNew = true;
@@ -119,19 +123,82 @@ public class IOTest {
             @Override
             public void call(Object... objects) {
                 System.out.println("connect:");
-                socket.send("hi");
+                socket.send("foo", "bar");
             }
         }).on(Socket.EVENT_MESSAGE, new Emitter.Listener() {
             @Override
             public void call(Object... objects) {
-                System.out.println("message: " + objects);
-                events.offer((String) objects[0]);
+                System.out.println(String.format(
+                        objects.length > 1 ? "message: %s, %s" : "message: %s", objects));
+                events.offer(objects);
             }
         });
         socket.connect();
 
-        assertThat(events.take(), is("hello client"));
-        assertThat(events.take(), is("hi"));
+        assertThat(events.take(), is(new Object[] {"hello client"}));
+        assertThat(events.take(), is(new Object[] {"foo", "bar"}));
+        socket.disconnect();
+    }
+
+    @Test(timeout = TIMEOUT)
+    public void event() throws URISyntaxException, InterruptedException {
+        final BlockingQueue<Object[]> events = new LinkedBlockingQueue<Object[]>();
+
+        Map<String, String> data = new HashMap<String, String>() {{
+            put("foo", "1");
+        }};
+        final JsonElement jsonData = new Gson().toJsonTree(data, Map.class);
+
+        IO.Options opts = new IO.Options();
+        opts.forceNew = true;
+        socket = IO.socket("http://localhost:" + PORT, opts);
+        socket.on(Socket.EVENT_CONNECT, new Emitter.Listener() {
+            @Override
+            public void call(Object... objects) {
+                System.out.println("connect:");
+                socket.emit("echo", jsonData, "bar");
+            }
+        }).on("echoBack", new Emitter.Listener() {
+            @Override
+            public void call(Object... objects) {
+                System.out.println(String.format("echoBack: %s, %s", objects));
+                events.offer(objects);
+            }
+        });
+        socket.connect();
+
+        assertThat(events.take(), is(new Object[] {jsonData, "bar"}));
+        socket.disconnect();
+    }
+
+    @Test(timeout = TIMEOUT)
+    public void ack() throws URISyntaxException, InterruptedException {
+        final BlockingQueue<Object[]> events = new LinkedBlockingQueue<Object[]>();
+
+        Map<String, String> data = new HashMap<String, String>() {{
+            put("foo", "1");
+        }};
+        final JsonElement jsonData = new Gson().toJsonTree(data, Map.class);
+
+        IO.Options opts = new IO.Options();
+        opts.forceNew = true;
+        socket = IO.socket("http://localhost:" + PORT, opts);
+        socket.on(Socket.EVENT_CONNECT, new Emitter.Listener() {
+            @Override
+            public void call(Object... objects) {
+                System.out.println("connect:");
+                socket.emit("ack", new Object[] {jsonData, "bar"}, new Socket.Ack() {
+                    @Override
+                    public void call(Object... args) {
+                        System.out.println(String.format("ack: %s, %s", args));
+                        events.offer(args);
+                    }
+                });
+            }
+        });
+        socket.connect();
+
+        assertThat(events.take(), is(new Object[] {jsonData, "bar"}));
         socket.disconnect();
     }
 }
diff --git a/src/test/resources/index.js b/src/test/resources/index.js
index ea558c0..7c2fd39 100644
--- a/src/test/resources/index.js
+++ b/src/test/resources/index.js
@@ -5,14 +5,23 @@ var server = require('http').Server()
 io.on('connection', function(socket) {
   socket.send('hello client');
 
-  socket.on('message', function(data) {
-    console.log('message:', data);
-    socket.send(data);
+  socket.on('message', function() {
+    var args = Array.prototype.slice.call(arguments);
+    console.log('message:', args);
+    socket.send.apply(socket, args);
   });
 
-  socket.on('echo', function(data) {
-    console.log('echo:', data);
-    socket.emit('echoBack', data);
+  socket.on('echo', function() {
+    var args = Array.prototype.slice.call(arguments);
+    console.log('echo:', args);
+    socket.emit.apply(socket, ['echoBack'].concat(args));
+  });
+
+  socket.on('ack', function() {
+    var args = Array.prototype.slice.call(arguments),
+        callback = args.pop();
+    console.log('ack:', args);
+    callback.apply(null, args);
   });
 
   socket.on('disconnect', function() {