diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,13 @@
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## 0.9.2
+### Removed
+- Disable unnecessary `-O2` optimisation added in previous version.
+
+### Added
+- Allow decoding unknown P2P messages.
+
 ## 0.9.1
 ### Added
 - Add a function to produce a structured signature over a transaction.
diff --git a/haskoin-core.cabal b/haskoin-core.cabal
--- a/haskoin-core.cabal
+++ b/haskoin-core.cabal
@@ -1,13 +1,13 @@
 cabal-version: 1.12
 
--- This file has been generated from package.yaml by hpack version 0.31.1.
+-- This file has been generated from package.yaml by hpack version 0.31.2.
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 571964654e85fdc471bd843a2c43a1debee35c14aca24a8cdba815efd5c09736
+-- hash: f8c182a15da9f3c4eb348dd84d0794720d0b89acf7981b7a317785f2e4196c96
 
 name:           haskoin-core
-version:        0.9.1
+version:        0.9.2
 synopsis:       Bitcoin & Bitcoin Cash library for Haskell
 description:    Haskoin Core is a complete Bitcoin and Bitcoin Cash library of functions and data types for Haskell developers.
 category:       Bitcoin, Finance, Network
@@ -80,7 +80,6 @@
       Paths_haskoin_core
   hs-source-dirs:
       src
-  ghc-options: -O2
   build-depends:
       QuickCheck
     , aeson
diff --git a/src/Network/Haskoin/Network/Common.hs b/src/Network/Haskoin/Network/Common.hs
--- a/src/Network/Haskoin/Network/Common.hs
+++ b/src/Network/Haskoin/Network/Common.hs
@@ -332,15 +332,15 @@
     Reject cmd code (VarString reason) B.empty
 
 instance Serialize Reject where
-
-    get = S.get >>= \(VarString bs) -> case stringToCommand bs of
-        Just cmd -> Reject cmd <$> S.get <*> S.get <*> maybeData
-        _ -> fail $ unwords
-            ["Reason get: Invalid message command" ,cs bs]
+    get =
+        S.get >>= \(VarString bs) ->
+            Reject (stringToCommand bs) <$> S.get <*> S.get <*> maybeData
       where
-        maybeData = isEmpty >>= \done ->
-            if done then return B.empty else getByteString 32
-
+        maybeData =
+            isEmpty >>= \done ->
+                if done
+                    then return B.empty
+                    else getByteString 32
     put (Reject cmd code reason dat) = do
         put $ VarString $ commandToString cmd
         put code
@@ -481,6 +481,7 @@
     | MCMempool
     | MCReject
     | MCSendHeaders
+    | MCOther ByteString
     deriving (Eq)
 
 instance Show MessageCommand where
@@ -489,51 +490,45 @@
 instance Read MessageCommand where
     readPrec = do
         String str <- lexP
-        maybe pfail return (stringToCommand (cs str))
+        return (stringToCommand (cs str))
 
 instance Serialize MessageCommand where
-    get = go =<< getByteString 12
+    get = go <$> getByteString 12
       where
         go bs =
             let str = unpackCommand bs
-            in case stringToCommand str of
-                Just cmd -> return cmd
-                Nothing  -> fail $ cs $
-                    "get MessageCommand: Invalid command: " <> str
+             in stringToCommand str
     put mc = putByteString $ packCommand $ commandToString mc
 
 instance IsString MessageCommand where
-    fromString str =
-        fromMaybe
-            (error ("Could not recognize message command " <> str))
-            (stringToCommand (cs str))
+    fromString str = stringToCommand (cs str)
 
 -- | Read a 'MessageCommand' from its string representation.
-stringToCommand :: ByteString -> Maybe MessageCommand
+stringToCommand :: ByteString -> MessageCommand
 stringToCommand str = case str of
-    "version"     -> Just MCVersion
-    "verack"      -> Just MCVerAck
-    "addr"        -> Just MCAddr
-    "inv"         -> Just MCInv
-    "getdata"     -> Just MCGetData
-    "notfound"    -> Just MCNotFound
-    "getblocks"   -> Just MCGetBlocks
-    "getheaders"  -> Just MCGetHeaders
-    "tx"          -> Just MCTx
-    "block"       -> Just MCBlock
-    "merkleblock" -> Just MCMerkleBlock
-    "headers"     -> Just MCHeaders
-    "getaddr"     -> Just MCGetAddr
-    "filterload"  -> Just MCFilterLoad
-    "filteradd"   -> Just MCFilterAdd
-    "filterclear" -> Just MCFilterClear
-    "ping"        -> Just MCPing
-    "pong"        -> Just MCPong
-    "alert"       -> Just MCAlert
-    "mempool"     -> Just MCMempool
-    "reject"      -> Just MCReject
-    "sendheaders" -> Just MCSendHeaders
-    _             -> Nothing
+    "version"     -> MCVersion
+    "verack"      -> MCVerAck
+    "addr"        -> MCAddr
+    "inv"         -> MCInv
+    "getdata"     -> MCGetData
+    "notfound"    -> MCNotFound
+    "getblocks"   -> MCGetBlocks
+    "getheaders"  -> MCGetHeaders
+    "tx"          -> MCTx
+    "block"       -> MCBlock
+    "merkleblock" -> MCMerkleBlock
+    "headers"     -> MCHeaders
+    "getaddr"     -> MCGetAddr
+    "filterload"  -> MCFilterLoad
+    "filteradd"   -> MCFilterAdd
+    "filterclear" -> MCFilterClear
+    "ping"        -> MCPing
+    "pong"        -> MCPong
+    "alert"       -> MCAlert
+    "mempool"     -> MCMempool
+    "reject"      -> MCReject
+    "sendheaders" -> MCSendHeaders
+    _             -> MCOther str
 
 -- | Convert a 'MessageCommand' to its string representation.
 commandToString :: MessageCommand -> ByteString
@@ -560,6 +555,7 @@
     MCMempool     -> "mempool"
     MCReject      -> "reject"
     MCSendHeaders -> "sendheaders"
+    MCOther c    -> c
 
 -- | Pack a string 'MessageCommand' so that it is exactly 12-bytes long.
 packCommand :: ByteString -> ByteString
diff --git a/src/Network/Haskoin/Network/Message.hs b/src/Network/Haskoin/Network/Message.hs
--- a/src/Network/Haskoin/Network/Message.hs
+++ b/src/Network/Haskoin/Network/Message.hs
@@ -18,6 +18,7 @@
     ) where
 
 import           Control.Monad                      (unless)
+import           Data.ByteString                    (ByteString)
 import qualified Data.ByteString                    as BS
 import           Data.Serialize                     (Serialize, encode, get,
                                                      put)
@@ -90,6 +91,7 @@
     | MMempool
     | MReject !Reject
     | MSendHeaders
+    | MOther !ByteString !ByteString
     deriving (Eq, Show)
 
 -- | Get 'MessageCommand' assocated with a message.
@@ -117,6 +119,7 @@
 msgType (MReject _)      = MCReject
 msgType MSendHeaders     = MCSendHeaders
 msgType MGetAddr         = MCGetAddr
+msgType (MOther c _)     = MCOther c
 
 -- | Deserializer for network messages.
 getMessage :: Network -> Get Message
@@ -149,7 +152,7 @@
                  MCPong        -> MPong <$> get
                  MCAlert       -> MAlert <$> get
                  MCReject      -> MReject <$> get
-                 _             -> fail $ "get: Invalid command " ++ show cmd
+                 MCOther c     -> MOther c <$> getByteString (fromIntegral len)
         else case cmd of
                  MCGetAddr     -> return MGetAddr
                  MCVerAck      -> return MVerAck
@@ -185,6 +188,7 @@
                 MMempool       -> (MCMempool, BS.empty)
                 MReject m      -> (MCReject, encode m)
                 MSendHeaders   -> (MCSendHeaders, BS.empty)
+                MOther c p     -> (MCOther c, p)
         chk = checkSum32 payload
         len = fromIntegral $ BS.length payload
         header = MessageHeader (getNetworkMagic net) cmd len chk
diff --git a/src/Network/Haskoin/Test/Network.hs b/src/Network/Haskoin/Test/Network.hs
--- a/src/Network/Haskoin/Test/Network.hs
+++ b/src/Network/Haskoin/Test/Network.hs
@@ -9,6 +9,7 @@
 module Network.Haskoin.Test.Network where
 
 import qualified Data.ByteString             as BS (empty, pack)
+import qualified Data.ByteString.Char8       as C8
 import           Data.Word                   (Word16, Word32)
 import           Network.Haskoin.Network
 import           Network.Haskoin.Test.Crypto
@@ -149,7 +150,8 @@
 
 -- | Arbitrary 'MessageCommand'.
 arbitraryMessageCommand :: Gen MessageCommand
-arbitraryMessageCommand =
+arbitraryMessageCommand = do
+    ASCIIString str <- arbitrary
     elements
         [ MCVersion
         , MCVerAck
@@ -170,4 +172,5 @@
         , MCPing
         , MCPong
         , MCAlert
+        , MCOther (C8.take 12 (C8.pack (filter (/= '\NUL') str)))
         ]
diff --git a/test/Network/Haskoin/NetworkSpec.hs b/test/Network/Haskoin/NetworkSpec.hs
--- a/test/Network/Haskoin/NetworkSpec.hs
+++ b/test/Network/Haskoin/NetworkSpec.hs
@@ -39,7 +39,7 @@
         it "encodes and decodes addr" $ property $ forAll arbitraryAddr1 cerealID
         it "encodes and decodes alert" $ property $ forAll arbitraryAlert cerealID
         it "encodes and decodes reject" $
-            property $forAll arbitraryReject cerealID
+            property $ forAll arbitraryReject cerealID
         it "encodes and decodes getdata" $
             property $ forAll arbitraryGetData cerealID
         it "encodes and decodes notfound" $