diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,7 @@
+2014-11-17 Rodrigo Setti <rodrigosetti@gmail.com>
+
+	* Fix the broken API due to the fact that messagepack is now using Int64
+
 2014-07-30 Rodrigo Setti <rodrigosetti@gmail.com>
 
 	* Parse request on demand (instead of waiting for the entire data)
diff --git a/Network/MessagePack.hs b/Network/MessagePack.hs
--- a/Network/MessagePack.hs
+++ b/Network/MessagePack.hs
@@ -13,6 +13,7 @@
 
 import Control.Applicative
 import Control.Monad
+import Data.Int
 import Data.MessagePack
 import Data.Maybe
 import Data.Serialize.Get
@@ -22,8 +23,8 @@
 import qualified Data.Serialize as S
 import qualified Data.Text as T
 
-type MsgId   = Int
-type MsgType = Int
+type MsgId   = Int64
+type MsgType = Int64
 
 reqMessage :: MsgType
 reqMessage = 0
@@ -31,7 +32,7 @@
 resMessage :: MsgType
 resMessage = 1
 
-errorMsgId :: Int
+errorMsgId :: Int64
 errorMsgId = 0
 
 -- | The type of a message pack RPC method. It gets an Object as a parameter, and
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -4,3 +4,78 @@
 
 [Message Pack](http://msgpack.org) RPC over TCP.
 
+Right now this implementation only supports TCP, but the plan is to support multiple transports ( UDP, UNIX domain sockets, _etc._)
+
+## MessagePack-RPC Protocol specification
+
+Reference: http://wiki.msgpack.org/display/MSGPACK/RPC+specification
+
+The protocol consists of "Request" message and the corresponding "Response" message. The server must send "Response" message in reply with the "Request" message.
+
+### Request Message
+
+The request message is a four elements array shown below, packed by MessagePack format.
+
+    [type, msgid, method, params]
+
+#### type
+
+Must be zero (integer). Zero means that this message is the "Request" message.
+
+#### msgid
+
+The 32-bit unsigned integer number. This number is used as a sequence number. The server replies with a requested msgid.
+
+#### method
+
+The string, which represents the method name.
+
+#### params
+
+The array of the function arguments. The elements of this array is arbitrary object.
+
+### Response Message
+
+The response message is a four elements array shown below, packed by MessagePack format.
+
+    [type, msgid, error, result]
+
+#### type
+
+Must be one (integer). One means that this message is the "Response" message.
+
+#### msgid
+
+The 32-bit unsigned integer number. This corresponds to the request message.
+
+#### error
+
+If the method is executed correctly, this field is Nil. If the error occurred at the server-side, then this field is an arbitrary object which represents the error.
+
+#### result
+
+An arbitrary object, which represents the returned result of the function. If error occurred, this field should be nil.
+
+### Notification Message (not yet supported)
+
+The notification message is a three elements array shown below, packed by MessagePack format.
+
+    [type, method, params]
+    
+#### type
+
+Must be two (integer). Two means that this message is the "Notification" message.
+
+#### method
+
+The string, which represents the method name.
+
+#### params
+
+The array of the function arguments. The elements of this array is arbitrary object.
+
+### The Order of the Response
+
+The server implementations don't need to send the reply, in the order of the received requests. If they receive the multiple messages, they can reply in random order.
+
+This is required for the pipelining. At the server side, some functions are fast, and some are not. If the server must reply with in order, the slow functions delay the other replies even if it's execution is already completed.
diff --git a/messagepack-rpc.cabal b/messagepack-rpc.cabal
--- a/messagepack-rpc.cabal
+++ b/messagepack-rpc.cabal
@@ -1,5 +1,5 @@
 name               : messagepack-rpc
-version            : 0.1.0.1
+version            : 0.1.0.2
 synopsis           : Message Pack RPC over TCP
 description        : Message Pack RPC over TCP
 homepage           : http://github.com/rodrigosetti/messagepack-rpc
@@ -26,7 +26,7 @@
                    , bytestring     == 0.10.*
                    , cereal         == 0.4.*
                    , containers     == 0.5.*
-                   , messagepack    == 0.2.*
+                   , messagepack    >= 0.2.1 && <= 0.2
                    , network-simple == 0.4.*
                    , text           == 1.*
   default-language : Haskell2010