diff --git a/nix-serve-ng.cabal b/nix-serve-ng.cabal
index d824e4d..b8d8c41 100644
--- a/nix-serve-ng.cabal
+++ b/nix-serve-ng.cabal
@@ -48,6 +48,7 @@ executable nix-serve
                     , base32
                     , bytestring
                     , charset
+                    , directory
                     , http-types
                     , managed
                     , megaparsec
diff --git a/src/Main.hs b/src/Main.hs
index f7f354d..f77f4ba 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -35,6 +35,7 @@ import qualified Network.Wai.Middleware.RequestLogger as RequestLogger
 import qualified Nix
 import qualified Options
 import qualified Options.Applicative                  as Options
+import qualified System.Directory                     as Directory
 import qualified System.Environment                   as Environment
 
 data ApplicationOptions = ApplicationOptions
@@ -250,6 +251,28 @@ makeApplication ApplicationOptions{..} request respond = do
 
                     done response
 
+                isPrivate <- not <$> liftIO (Directory.doesPathExist (ByteString.Char8.unpack storePath ++ "/.private"))
+                let sockAddr = Wai.remoteHost request
+                hostAddr  <- case sockAddr of
+                    SockAddrInet _ host -> return host
+                    _ -> return $ Socket.tupleToHostAddress (255, 255, 255, 255)
+
+                let isInternalClient = hostAddr >= Socket.tupleToHostAddress (10, 0, 0, 0) && hostAddr < Socket.tupleToHostAddress (11, 0, 0, 0)
+
+                Monad.unless (isInternalClient || not isPrivate) do
+                    let headers = [ ("Content-Type", "text/plain") ]
+
+                    let builder = "Forbbiden.\n"
+
+                    let response =
+                            Wai.responseBuilder
+                                    Types.status403
+                                    headers
+                                    builder
+
+                    done response
+
+
                 let streamingBody write flush = do
                        result <- Nix.dumpPath hashPart callback