diff --git a/CHANGES b/CHANGES
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,8 @@
+0.3.14
+
+* Fix `Tree` bug.
+* Add `UUID` instances.
+
 0.3.13
 
 Author: Oleg Grenrus <oleg.grenrus@iki.fi>
diff --git a/quickcheck-instances.cabal b/quickcheck-instances.cabal
--- a/quickcheck-instances.cabal
+++ b/quickcheck-instances.cabal
@@ -1,5 +1,5 @@
 Name:                quickcheck-instances
-Version:             0.3.13
+Version:             0.3.14
 Synopsis:            Common quickcheck instances
 Description:         QuickCheck instances.
                      .
@@ -25,7 +25,7 @@
 Category:            Testing
 Build-type:          Simple
 Extra-source-files:  CHANGES
-Cabal-version:       >=1.6
+Cabal-version:       >=1.8
 Tested-With:
   GHC==7.4.2,
   GHC==7.6.3,
@@ -49,16 +49,28 @@
                        case-insensitive >=1.2.0.4 && <1.3,
                        containers >= 0.3 && < 0.6,
                        hashable >= 1.1.2.3 && < 1.3,
-                       unordered-containers >= 0.2.1 && < 0.3,
                        old-time >= 1.0 && < 1.2,
                        QuickCheck >= 2.1 && < 2.10,
+                       scientific >=0.2 && <0.4,
                        tagged >= 0.8.5 && <0.9,
                        text >= 0.7 && < 1.3,
                        time >= 1.1 && < 1.9,
-                       vector >= 0.9 && <0.13,
-                       scientific >=0.2 && <0.4
+                       unordered-containers >= 0.2.1 && < 0.3,
+                       uuid-types >=1.0.3 && <1.1,
+                       vector >= 0.9 && <0.13
 
   Ghc-options:         -Wall
   Other-modules:       Test.QuickCheck.Instances.LegacyNumeric
   -- Build-tools:
 
+test-suite self-test
+  type: exitcode-stdio-1.0
+  main-is: Tests.hs
+  hs-source-dirs: test
+  build-depends:
+    base,
+    QuickCheck,
+    quickcheck-instances,
+    containers,
+    tagged,
+    uuid-types
diff --git a/src/Test/QuickCheck/Instances.hs b/src/Test/QuickCheck/Instances.hs
--- a/src/Test/QuickCheck/Instances.hs
+++ b/src/Test/QuickCheck/Instances.hs
@@ -38,6 +38,7 @@
 import Data.Ratio
 import Test.QuickCheck
 import Test.QuickCheck.Function
+import Data.Word (Word32)
 
 import qualified Data.Array.IArray as Array
 import qualified Data.Array.Unboxed as Array
@@ -64,7 +65,10 @@
 import qualified Data.Vector.Generic as GVector
 import qualified Data.Vector.Unboxed as UVector
 import qualified System.Time as OldTime
+import qualified Data.UUID.Types as UUID
 
+import Debug.Trace
+
 import Test.QuickCheck.Instances.LegacyNumeric()
 
 -- Array
@@ -250,17 +254,18 @@
 instance Arbitrary a => Arbitrary (Tree.Tree a) where
     arbitrary = sized $ \n -> do -- Sized is the size of the trees.
         value <- arbitrary
-        pars <- arbPartition (n - 1)
+        pars <- arbPartition (n - 1) -- can go negative!
         forest <- forM pars $ \i -> resize i arbitrary
         return $ Tree.Node value forest
       where
         arbPartition :: Int -> Gen [Int]
-        arbPartition 0 = pure []
-        arbPartition 1 = pure [1]
-        arbPartition k = do
-            first <- elements [1..k]
-            rest <- arbPartition $ k - first
-            return $ first : rest
+        arbPartition k = case compare k 1 of
+            LT -> pure []
+            EQ -> pure [1]
+            GT -> do
+                first <- elements [1..k]
+                rest <- arbPartition $ k - first
+                return $ first : rest
 
     shrink (Tree.Node val forest) =
          forest ++ [Tree.Node e fs | (e, fs) <- shrink (val, forest)]
@@ -518,3 +523,19 @@
 
 instance Function b => Function (Tagged.Tagged a b) where
     function = functionMap Tagged.unTagged Tagged.Tagged
+
+-- uuid
+
+uuidFromWords :: (Word32, Word32, Word32, Word32) -> UUID.UUID
+uuidFromWords (a,b,c,d) = UUID.fromWords a b c d
+
+-- | Uniform distribution.
+instance Arbitrary UUID.UUID where
+    arbitrary = uuidFromWords <$> arbitrary
+    shrink = map uuidFromWords . shrink . UUID.toWords
+
+instance CoArbitrary UUID.UUID where
+    coarbitrary = coarbitrary . UUID.toWords
+
+instance Function UUID.UUID where
+    function = functionMap UUID.toWords uuidFromWords
diff --git a/test/Tests.hs b/test/Tests.hs
new file mode 100644
--- /dev/null
+++ b/test/Tests.hs
@@ -0,0 +1,22 @@
+module Main (main) where
+
+import Data.Proxy (Proxy (..))
+import Test.QuickCheck
+import Test.QuickCheck.Instances ()
+
+import qualified Data.Tree as Tree
+import           Data.UUID.Types (UUID)
+
+-- | Example law: == (and thus ===) should be reflexive.
+eqReflexive
+    :: (Eq a, Show a)
+    => Proxy a
+    -> a
+    -> Property
+eqReflexive _ x = x === x
+
+main :: IO ()
+main = do
+    quickCheck $ eqReflexive (Proxy :: Proxy Int)
+    quickCheck $ eqReflexive (Proxy :: Proxy (Tree.Tree Int))
+    quickCheck $ eqReflexive (Proxy :: Proxy UUID)