diff --git a/CHANGES.txt b/CHANGES.txt
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,5 +1,10 @@
 Changelog for Extra
 
+1.4.11
+    Require QuickCheck 2.9
+    #23, deprecate offsetTimeIncrease and subtract
+    #22, improve offsetTime to give reliable measurements
+    Depend on the clock library
 1.4.10
     Add Data.Typeable.Extra containing typeRep, Proxy, (:~:)
 1.4.9
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -30,3 +30,5 @@
 * base 4.6 == GHC 7.6
 * base 4.5 == GHC 7.4
 * base 4.4 == GHC 7.2
+
+A more complete list can be found [here](https://wiki.haskell.org/Base_package#Versions).
diff --git a/extra.cabal b/extra.cabal
--- a/extra.cabal
+++ b/extra.cabal
@@ -1,7 +1,7 @@
 cabal-version:      >= 1.10
 build-type:         Simple
 name:               extra
-version:            1.4.10
+version:            1.4.11
 license:            BSD3
 license-file:       LICENSE
 category:           Development
@@ -35,6 +35,7 @@
         directory,
         filepath,
         process,
+        clock >= 0.7,
         time
     if !os(windows)
         build-depends: unix
@@ -66,8 +67,9 @@
         directory,
         filepath,
         extra,
+        clock >= 0.7,
         time,
-        QuickCheck
+        QuickCheck >= 2.9
     if !os(windows)
         build-depends: unix
     hs-source-dirs: test
diff --git a/src/System/Time/Extra.hs b/src/System/Time/Extra.hs
--- a/src/System/Time/Extra.hs
+++ b/src/System/Time/Extra.hs
@@ -15,6 +15,7 @@
 
 import Control.Concurrent
 import Data.Time.Clock
+import System.Clock
 import Numeric.Extra
 import Data.IORef
 import Control.Monad.Extra
@@ -72,11 +73,11 @@
                             (\_ -> fmap Just f))
 
 
+{-# DEPRECATED subtractTime "Function is being retired - use diffUTCTime directly." #-}
+
 -- | Calculate the difference between two times in seconds.
 --   Usually the first time will be the end of an event, and the
 --   second time will be the beginning.
---
--- > \a b -> a > b ==> subtractTime a b > 0
 subtractTime :: UTCTime -> UTCTime -> Seconds
 subtractTime end start = fromRational $ toRational $ end `diffUTCTime` start
 
@@ -98,19 +99,21 @@
             where (ms,ss) = round x `divMod` 60
 
 
--- | Call once to start, then call repeatedly to get the elapsed time since the first
---   call. Values will usually increase, unless the system clock is updated
---   (if you need the guarantee, see 'offsetTimeIncrease').
+-- | Call once to start, then call repeatedly to get the elapsed time since the first call.
+--   The time is guaranteed to be monotonic. This function is robust to system time changes.
+--
+-- > do f <- offsetTime; xs <- replicateM 10 f; return $ xs == sort xs
 offsetTime :: IO (IO Seconds)
 offsetTime = do
-    start <- getCurrentTime
+    start <- time
     return $ do
-        end <- getCurrentTime
-        return $ end `subtractTime` start
+        end <- time
+        return $ 1e-9 * fromIntegral (toNanoSecs $ end - start)
+    where time = getTime Monotonic
 
--- | Like 'offsetTime', but results will never decrease (though they may stay the same).
---
--- > do f <- offsetTimeIncrease; xs <- replicateM 10 f; return $ xs == sort xs
+{-# DEPRECATED offsetTimeIncrease "Use offsetTime instead, which is guaranteed to always increase." #-}
+
+-- | A synonym for 'offsetTime'.
 offsetTimeIncrease :: IO (IO Seconds)
 offsetTimeIncrease = do
     t <- offsetTime
@@ -120,6 +123,8 @@
         atomicModifyIORef ref $ \o -> let m = max t o in m `seq` (m, m)
 
 -- | Record how long a computation takes in 'Seconds'.
+--
+-- > do (a,_) <- duration $ sleep 1; return $ a >= 1 && a <= 1.1
 duration :: IO a -> IO (Seconds, a)
 duration act = do
     time <- offsetTime
diff --git a/test/TestGen.hs b/test/TestGen.hs
--- a/test/TestGen.hs
+++ b/test/TestGen.hs
@@ -232,9 +232,9 @@
     testGen "timeout 0.1  (print 1) == fmap Just (print 1)" $ timeout 0.1  (print 1) == fmap Just (print 1)
     testGen "do (t, _) <- duration $ timeout 0.1 $ sleep 1000; print t; return $ t < 1" $ do (t, _) <- duration $ timeout 0.1 $ sleep 1000; print t; return $ t < 1
     testGen "timeout 0.1  (sleep 2 >> print 1) == return Nothing" $ timeout 0.1  (sleep 2 >> print 1) == return Nothing
-    testGen "\\a b -> a > b ==> subtractTime a b > 0" $ \a b -> a > b ==> subtractTime a b > 0
     testGen "showDuration 3.435   == \"3.44s\"" $ showDuration 3.435   == "3.44s"
     testGen "showDuration 623.8   == \"10m24s\"" $ showDuration 623.8   == "10m24s"
     testGen "showDuration 62003.8 == \"17h13m\"" $ showDuration 62003.8 == "17h13m"
     testGen "showDuration 1e8     == \"27777h47m\"" $ showDuration 1e8     == "27777h47m"
-    testGen "do f <- offsetTimeIncrease; xs <- replicateM 10 f; return $ xs == sort xs" $ do f <- offsetTimeIncrease; xs <- replicateM 10 f; return $ xs == sort xs
+    testGen "do f <- offsetTime; xs <- replicateM 10 f; return $ xs == sort xs" $ do f <- offsetTime; xs <- replicateM 10 f; return $ xs == sort xs
+    testGen "do (a,_) <- duration $ sleep 1; return $ a >= 1 && a <= 1.1" $ do (a,_) <- duration $ sleep 1; return $ a >= 1 && a <= 1.1
diff --git a/test/TestUtil.hs b/test/TestUtil.hs
--- a/test/TestUtil.hs
+++ b/test/TestUtil.hs
@@ -70,11 +70,9 @@
 
 instance Testable () where
     property = property . (`seq` True)
-    exhaustive _ = True
 
 instance Testable a => Testable (IO a) where
     property = property . unsafePerformIO
-    exhaustive = exhaustive . unsafePerformIO
 
 instance Eq a => Eq (IO a) where
     a == b = unsafePerformIO $ do
@@ -104,6 +102,3 @@
 
 instance Arbitrary DiffTime where
     arbitrary = fmap realToFrac $ choose (0 :: Double, 86401)
-
-instance Arbitrary Version where
-    arbitrary = makeVersion . map abs <$> listOf1 arbitrary