diff --git a/datetime-sb.cabal b/datetime-sb.cabal
--- a/datetime-sb.cabal
+++ b/datetime-sb.cabal
@@ -1,5 +1,5 @@
 name:                datetime-sb
-version:             0.2.3
+version:             0.2.4
 stability:           experimental
 Description:
   Provides several utilities for easily converting among the
@@ -34,6 +34,7 @@
   type: exitcode-stdio-1.0
   hs-source-dirs: test
   main-is: Suite.hs
+  other-modules: Data.DateTimeTest
   build-depends:
       datetime-sb
 
diff --git a/test/Data/DateTimeTest.hs b/test/Data/DateTimeTest.hs
new file mode 100644
--- /dev/null
+++ b/test/Data/DateTimeTest.hs
@@ -0,0 +1,51 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Data.DateTimeTest where
+
+import Test.Framework
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+import Test.QuickCheck
+import Data.Maybe (fromJust)
+
+import Data.Time.Clock (UTCTime)
+import Data.DateTime
+
+instance Arbitrary UTCTime where
+    arbitrary       = do
+        offset <- choose (0, 20000) :: Gen Float
+        return . fromMJD' $ offset + fromRational startOfTimeMJD
+
+
+tests :: [Test]
+tests = [ testGroup "properties"
+          [ testProperty "MJD" prop_MJD
+          , testProperty "Universal" prop_Universal
+          , testProperty "StartOfTime" prop_StartOfTime
+          , testProperty "SqlString" prop_SqlString
+          -- , testProperty "SqlStartOfTime" prop_SqlStartOfTime
+          ]
+        ]
+
+invariant :: Eq a => (a -> a) -> a -> Bool
+invariant f x = f x == x
+
+prop_MJD :: DateTime -> Bool
+prop_MJD  = invariant $ fromMJD  . toMJD
+
+prop_MJD' :: DateTime -> Bool
+prop_MJD' = invariant $ fromMJD' . toMJD'
+
+prop_Universal :: DateTime -> Bool
+prop_Universal = invariant $ fromUniversalTime . toUniversalTime
+
+prop_StartOfTime :: DateTime -> Bool
+prop_StartOfTime _ = toSeconds startOfTime == 0
+
+prop_SqlString :: DateTime -> Bool
+prop_SqlString dt = (fromJust . fromSqlString . toSqlString $ dt') == dt'
+  where
+    Just dt' = fromSqlString . toSqlString $ dt
+
+-- It doesn't seem like this test ever passed, so disabling.
+-- prop_SqlStartOfTime :: DateTime -> Bool
+-- prop_SqlStartOfTime _ = toSqlString startOfTime == "1970-01-01 00:00:00"