bug in addToClockTime

The Glorious Glasgow Haskell Compilation System, version 6.4.3.20060816

> now <- getClockTime
> addToClockTime (TimeDiff {tdYear = 0, tdMonth = 0, tdDay = 0, tdHour = 0, 
> tdMin = 0, tdSec = 0, tdPicosec = 999999999999}) now
*** Exception: Time.toClockTime: picoseconds out of range

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