Cannot derive a Show instance for data containing UTCTime

I have data defined like the ff.:

import Data.Time.Clock

data D = D { ...,
             someDate :: UTCTime,
             ... }
         deriving (Eq, Show)

When I compile it, I get the ff. error:

No instance for (Show UTCTime)
  arising from the 'deriving' clause of a data type declaration
               at ...

I already have the time-1.1.3 package which should already have this instance according to documentation. My GHC version is 6.8.2.