diff --git a/Database/Persist/MongoDB.hs b/Database/Persist/MongoDB.hs
--- a/Database/Persist/MongoDB.hs
+++ b/Database/Persist/MongoDB.hs
@@ -116,25 +116,40 @@
     parseJSON (Number (D x)) = (return . NoOrphanNominalDiffTime . fromRational . toRational) x
     parseJSON _ = fail "couldn't parse diff time"
 
-instance FromJSON PortID where
-    parseJSON (Number (I x)) = (return . PortNumber . fromInteger) x
+newtype NoOrphanPortID = NoOrphanPortID PortID deriving (Show, Eq)
+
+instance FromJSON NoOrphanPortID where
+    parseJSON (Number (I x)) = (return . NoOrphanPortID . PortNumber . fromInteger) x
     parseJSON _ = fail "couldn't parse port number"
 
+
 data Connection = Connection DB.Pipe DB.Database
 type ConnectionPool = Pool.Pool Connection
 
+-- | ToPathPiece is used to convert a key to/from text
 instance PathPiece (KeyBackend MongoBackend entity) where
-    toPathPiece (Key pOid@(PersistObjectId _)) = -- T.pack $ show $ Serialize.encode bsonId
-        let oid = persistObjectIdToDbOid pOid
-        in  T.pack $ show oid
-    toPathPiece k = throw $ PersistInvalidField $ T.pack $ "Invalid Key (expected PersistObjectId): " ++ show k
+    toPathPiece = keyToText
+    fromPathPiece keyText = readMayKey $
+        -- handle a JSON type prefix
+        -- 'o' is a non-hex character, so no confusion here
+        case T.uncons keyText of
+            Just ('o', prefixed) -> prefixed
+            _ -> keyText
 
-    fromPathPiece str =
-      case (reads $ (T.unpack str))::[(DB.ObjectId,String)] of
-        (parsed,_):[] -> Just $ Key $ PersistObjectId $ Serialize.encode parsed
-        _ -> Nothing
+keyToText :: KeyBackend MongoBackend entity -> Text
+keyToText (Key pOid@(PersistObjectId _)) = -- T.pack $ show $ Serialize.encode bsonId
+    let oid = persistObjectIdToDbOid pOid
+    in  T.pack $ show oid
+keyToText k = throw $ PersistInvalidField $ T.pack $ "Invalid Key (expected PersistObjectId): " ++ show k
 
+-- | Convert a Text to a Key
+readMayKey :: Text -> Maybe (KeyBackend MongoBackend entity)
+readMayKey str =
+  case (reads $ (T.unpack str)) :: [(DB.ObjectId,String)] of
+    (parsed,_):[] -> Just $ Key $ PersistObjectId $ Serialize.encode parsed
+    _ -> Nothing
 
+
 withMongoDBConn :: (Trans.MonadIO m, Applicative m)
                 => Database -> HostName -> PortID
                 -> Maybe MongoAuth -> NominalDiffTime
@@ -209,19 +224,22 @@
 runMongoDBPoolDef :: (Trans.MonadIO m, MonadBaseControl IO m) => DB.Action m a -> ConnectionPool -> m a
 runMongoDBPoolDef = runMongoDBPool (DB.ConfirmWrites ["j" DB.=: True])
 
-filterByKey :: (PersistEntity record) => KeyBackend MongoBackend record -> DB.Document
-filterByKey key = [_id DB.=: keyToOid key]
+filterByKey :: (PersistEntity record, PersistEntityBackend record ~ MongoBackend)
+            => Key record -> DB.Document
+filterByKey k = [_id DB.=: keyToOid k]
 
-queryByKey :: (PersistEntity record) => KeyBackend MongoBackend record -> EntityDef a -> DB.Query 
-queryByKey key entDef = (DB.select (filterByKey key) (unDBName $ entityDB entDef)) 
+queryByKey :: (PersistEntity record, PersistEntityBackend record ~ MongoBackend)
+           => Key record -> EntityDef a -> DB.Query
+queryByKey k record = (DB.select (filterByKey k) (unDBName $ entityDB record))
 
-selectByKey :: (PersistEntity record) => KeyBackend MongoBackend record -> EntityDef a -> DB.Selection 
-selectByKey k entDef = (DB.select (filterByKey k) (unDBName $ entityDB entDef))
+selectByKey :: (PersistEntity record, PersistEntityBackend record ~ MongoBackend)
+            => Key record -> EntityDef a -> DB.Selection
+selectByKey k record = (DB.select (filterByKey k) (unDBName $ entityDB record))
 
-updateFields :: (PersistEntity val) => [Update val] -> [DB.Field]
+updateFields :: (PersistEntity entity) => [Update entity] -> [DB.Field]
 updateFields upds = map updateToMongoField upds 
 
-updateToMongoField :: (PersistEntity val) => Update val -> DB.Field
+updateToMongoField :: (PersistEntity entity) => Update entity -> DB.Field
 updateToMongoField (Update field v up) =
     opName DB.:= DB.Doc [( (unDBName $ fieldDB $ persistFieldDef field) DB.:= opValue)]
     where 
@@ -277,12 +295,12 @@
 fieldToLabel :: FieldDef a -> Text
 fieldToLabel = unDBName . fieldDB
 
-saveWithKey :: forall m record keyEntity. -- (Applicative m, Functor m, MonadBaseControl IO m,
-                                    (PersistEntity keyEntity, PersistEntity record)
-            => (record -> [DB.Field])
-            -> (DB.Collection -> DB.Document -> DB.Action m () )
-            -> KeyBackend MongoBackend keyEntity
-            -> record
+saveWithKey :: forall m entity keyEntity.
+            (PersistEntity entity, PersistEntity keyEntity, PersistEntityBackend keyEntity ~ MongoBackend)
+            => (entity -> [DB.Field])
+            -> (Text -> [DB.Field] -> DB.Action m ())
+            -> Key keyEntity
+            -> entity
             -> DB.Action m ()
 saveWithKey entToFields dbSave key record =
       dbSave (collectionName record) ((keyToMongoIdField key):(entToFields record))
@@ -348,7 +366,8 @@
 _id :: T.Text
 _id = "_id"
 
-keyToMongoIdField :: PersistEntity val => KeyBackend MongoBackend val -> DB.Field
+keyToMongoIdField :: (PersistEntity entity, PersistEntityBackend entity ~ MongoBackend)
+                  => Key entity -> DB.Field
 keyToMongoIdField k = _id DB.:= (DB.ObjId $ keyToOid k)
 
 
@@ -622,7 +641,7 @@
 oidToPersistValue :: DB.ObjectId -> PersistValue
 oidToPersistValue =  PersistObjectId . Serialize.encode
 
-oidToKey :: (PersistEntity val) => DB.ObjectId -> KeyBackend MongoBackend val
+oidToKey :: (PersistEntity entity) => DB.ObjectId -> Key entity
 oidToKey = Key . oidToPersistValue
 
 persistObjectIdToDbOid :: PersistValue -> DB.ObjectId
@@ -631,7 +650,8 @@
                   Right o -> o
 persistObjectIdToDbOid _ = throw $ PersistInvalidField "expected PersistObjectId"
 
-keyToOid :: (PersistEntity val) => KeyBackend MongoBackend val -> DB.ObjectId
+keyToOid :: (PersistEntity entity, PersistEntityBackend entity ~ MongoBackend)
+         => Key entity -> DB.ObjectId
 keyToOid (Key k) = persistObjectIdToDbOid k
 
 instance DB.Val PersistValue where
@@ -718,7 +738,7 @@
     loadConfig (Object o) = do
         db                 <- o .:  "database"
         host               <- o .:? "host" .!= "127.0.0.1"
-        port               <- o .:? "port" .!= DB.defaultPort
+        (NoOrphanPortID port) <- o .:? "port" .!= (NoOrphanPortID DB.defaultPort)
         poolStripes        <- o .:? "poolstripes" .!= 1
         stripeConnections  <- o .:  "connections"
         (NoOrphanNominalDiffTime connectionIdleTime) <- o .:? "connectionIdleTime" .!= 20
diff --git a/persistent-mongoDB.cabal b/persistent-mongoDB.cabal
--- a/persistent-mongoDB.cabal
+++ b/persistent-mongoDB.cabal
@@ -1,5 +1,5 @@
 name:            persistent-mongoDB
-version:         1.2.1
+version:         1.2.1.1
 license:         MIT
 license-file:    LICENSE
 author:          Greg Weber <greg@gregweber.info>