Why does System.Timeout in Haskell not work for sockets?

I'm trying to listen for UDP Datagrams for just 3 seconds in Haskell. I wrote some code but I'm not sure why it's not working. I set the timeout to 3 seconds, but it just waits forever and doesn't block

import Control.Concurrent  as CC  (forkIO, threadDelay, killThread)
import qualified Data.ByteString.Char8 as C
import Network.Socket 
import Network.Socket.ByteString as B
import Data.IORef
import Control.Monad            (forever)
import System.Timeout

receiveDatagram = do 
  ack <- newIORef (0 :: Int) 
  addrinfos <- getAddrInfo Nothing (Just "127.0.0.1") (Just "7001")
  let serveraddr = head addrinfos
  sock <- socket (addrFamily serveraddr) Datagram defaultProtocol
  bind sock (addrAddress serveraddr)
  print "starting"
  tmp <- timeout 3000000 (do
    (msg, addr) <- B.recvFrom sock 1024
    close sock
    writeIORef ack 1
    print msg
    )
  case tmp of 
    Nothing -> close sock
    _       -> print "something else"
  print "timeout done"

The documentation for timeout states:

Standard I/O functions like hGetBuf, hPutBuf, Network.Socket.accept, or hWaitForInput appear to be blocking, but they really don't because the runtime system uses scheduling mechanisms like select(2) to perform asynchronous I/O, so it is possible to interrupt standard socket I/O or file I/O using this combinator.