Dear Haskellers, I am baffled by a strange bug (?) with threadDelay on Windows. It delays for less time than expected (500 seconds vs expected 24 hours), and is consistently reproducible on my system. Can someone have a look (need some patience, ~8 minutes waiting), just to be sure? I glanced around trac but didn't find any related issues. How to reproduce: module Main where import Data.Time import Control.Concurrent import Control.Monad main :: IO () main = do _ <- forkIO thread getLine >>= print -- Just to keep the main thread running thread :: IO () thread = forever $ do now <- getCurrentTime print now threadDelay 86400000000 print "done waiting" Expected result: 2016-12-28 13:07:49.5113098 UTC ... (next timing should be the next day 2016-12-29) Actual result: 2016-12-28 13:07:49.5113098 UTC "done waiting" 2016-12-28 13:16:10.2159485 UTC "done waiting" 2016-12-28 13:24:30.8735845 UTC "done waiting" 2016-12-28 13:32:51.5292203 UTC ... System: Windows 7 Enterprise Service Pack 1, ghc 7.10.3 This seems specific to Windows, it doesn't appear on Debian 8. Help is appreciated! Regards, Hon Rant: It has cost me significant debugging time! Please tell me I made a rookie mistake or misread the docs somewhere!