diff --git a/Statistics/Test/StudentT.hs b/Statistics/Test/StudentT.hs
--- a/Statistics/Test/StudentT.hs
+++ b/Statistics/Test/StudentT.hs
@@ -134,16 +134,16 @@
 
 
 -- Calculate T-statistics for paired sample
-tStatisticsPaired :: (G.Vector v (Double, Double), G.Vector v Double)
+tStatisticsPaired :: (G.Vector v (Double, Double))
                   => v (Double, Double)
                   -> (Double, Double)
 {-# INLINE tStatisticsPaired #-}
 tStatisticsPaired sample = (t, ndf)
   where
     -- t-statistics
-    t = let d    = G.map (uncurry (-)) sample
-            sumd = G.sum d
-        in sumd / sqrt ((n * G.sum (G.map square d) - square sumd) / ndf)
+    t = let d    = U.map (uncurry (-)) $ G.convert sample
+            sumd = U.sum d
+        in sumd / sqrt ((n * U.sum (U.map square d) - square sumd) / ndf)
     -- degree of freedom
     ndf = n - 1
     n   = fromIntegral $ G.length sample
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,10 @@
+## Changes in 0.16.2.1
+
+ * Unnecessary constraint dropped from `tStatisticsPaired`.
+
+ * Compatibility with QuickCheck-2.14. Test suite doesn't fail every time.
+
+
 ## Changes in 0.16.2.0
 
  * Improved precision for `complCumulative` for hypergeometric and binomial
diff --git a/statistics.cabal b/statistics.cabal
--- a/statistics.cabal
+++ b/statistics.cabal
@@ -1,5 +1,5 @@
 name:           statistics
-version:        0.16.2.0
+version:        0.16.2.1
 synopsis:       A library of statistical types, data, and functions
 description:
   This library provides a number of common functions and types useful
@@ -46,14 +46,15 @@
   tests/utils/fftw.c
 
 tested-with:
-    GHC ==8.0.2
-     || ==8.2.2
-     || ==8.4.4
-     || ==8.6.5
-     || ==8.8.4
-     || ==8.10.7
-     || ==9.0.1
-     || ==9.2.1
+    GHC ==8.4.4
+    GHC ==8.6.5
+    GHC ==8.8.4
+    GHC ==8.10.7
+    GHC ==9.0.2
+    GHC ==9.2.8
+    GHC ==9.4.6
+    GHC ==9.6.2
+
 
 library
   default-language: Haskell2010
diff --git a/tests/Tests/Correlation.hs b/tests/Tests/Correlation.hs
--- a/tests/Tests/Correlation.hs
+++ b/tests/Tests/Correlation.hs
@@ -5,11 +5,11 @@
 
 import Control.Arrow (Arrow(..))
 import qualified Data.Vector as V
+import Data.Maybe
 import Statistics.Correlation
 import Statistics.Correlation.Kendall
-import Test.QuickCheck ((==>),Property,counterexample)
 import Test.Tasty
-import Test.Tasty.QuickCheck
+import Test.Tasty.QuickCheck hiding (sample)
 import Test.Tasty.HUnit
 
 import Tests.ApproxEq
@@ -34,15 +34,19 @@
 
 testPearson :: [(Double,Double)] -> Property
 testPearson sample
-  = (length sample > 1) ==> (exact ~= fast)
+  = (length sample > 1 && isJust exact) ==> (case exact of
+                                               Just e  -> e ~= fast
+                                               Nothing -> property False
+                                            )
   where
     (~=) = eql 1e-12
     exact = exactPearson $ map (realToFrac *** realToFrac) sample
     fast  = pearson $ V.fromList sample
 
-exactPearson :: [(Rational,Rational)] -> Double
+exactPearson :: [(Rational,Rational)] -> Maybe Double
 exactPearson sample
-  = realToFrac cov / sqrt (realToFrac (varX * varY))
+  | varX == 0 || varY == 0 = Nothing
+  | otherwise              = Just $ realToFrac cov / sqrt (realToFrac (varX * varY))
   where
     (xs,ys) = unzip sample
     n       = fromIntegral $ length sample
diff --git a/tests/Tests/Distribution.hs b/tests/Tests/Distribution.hs
--- a/tests/Tests/Distribution.hs
+++ b/tests/Tests/Distribution.hs
@@ -348,7 +348,7 @@
   quantileIsInvCDF_enabled _ = False
   -- We compute CDF and complement using same method so precision
   -- should be very good here.
-  prec_complementCDF _ = 2 * m_epsilon
+  prec_complementCDF _ = 64 * m_epsilon
 
 instance Param ChiSquared where
   prec_quantile_CDF _ = (32,32)
@@ -367,7 +367,7 @@
   -- introduced by exp . logGamma.  This could only be fixed in
   -- math-function by implementing gamma
   prec_quantile_CDF _ = (24,24)
-  prec_logDensity   _ = 64
+  prec_logDensity   _ = 512
 instance Param GeometricDistribution
 instance Param GeometricDistribution0
 instance Param HypergeometricDistribution
diff --git a/tests/Tests/Matrix.hs b/tests/Tests/Matrix.hs
--- a/tests/Tests/Matrix.hs
+++ b/tests/Tests/Matrix.hs
@@ -5,7 +5,6 @@
 import Test.Tasty (TestTree, testGroup)
 import Test.Tasty.QuickCheck (testProperty)
 import Test.QuickCheck
-import Tests.ApproxEq (ApproxEq(..))
 import Tests.Matrix.Types
 import qualified Data.Vector.Unboxed as U
 
@@ -27,9 +26,20 @@
 t_transpose m = U.concat (map (column n) [0..rows m-1]) === toVector m
   where n = transpose m
 
-t_qr :: Matrix -> Property
-t_qr a = hasNaN p .||. eql 1e-10 a p
-  where p = uncurry multiply (qr a)
+t_qr :: Property
+t_qr = property $ do
+  a <- do (r,c) <- arbitrary
+          fromMat <$> arbMatWith r c (fromIntegral <$> choose (-10, 10::Int))
+  let (q,r) = qr a
+      a'    = multiply q r
+  pure $ counterexample ("A  = \n"++show a)
+       $ counterexample ("A' = \n"++show a')
+       $ counterexample ("Q  = \n"++show q)
+       $ counterexample ("R  = \n"++show r)
+       $ dimension a == dimension a'
+      && ( hasNaN a'
+        || and (zipWith (\x y -> abs (x - y) < 1e-12) (toList a) (toList a'))
+         )
 
 tests :: TestTree
 tests = testGroup "Matrix"
diff --git a/tests/Tests/Matrix/Types.hs b/tests/Tests/Matrix/Types.hs
--- a/tests/Tests/Matrix/Types.hs
+++ b/tests/Tests/Matrix/Types.hs
@@ -6,6 +6,8 @@
       Mat(..)
     , fromMat
     , toMat
+    , arbMat
+    , arbMatWith
     ) where
 
 import Control.Monad (join)
@@ -32,10 +34,21 @@
     arbitrary = small $ join (arbMat <$> arbitrary <*> arbitrary)
     shrink (Mat r c xs) = Mat r c <$> shrinkFixedList (shrinkFixedList shrink) xs
 
-arbMat :: (Arbitrary a) => Positive (Small Int) -> Positive (Small Int)
-       -> Gen (Mat a)
-arbMat (Positive (Small r)) (Positive (Small c)) =
-    Mat r c <$> vectorOf r (vector c)
+arbMat
+  :: (Arbitrary a)
+  => Positive (Small Int)
+  -> Positive (Small Int)
+  -> Gen (Mat a)
+arbMat r c = arbMatWith r c arbitrary
+
+arbMatWith
+  :: (Arbitrary a)
+  => Positive (Small Int)
+  -> Positive (Small Int)
+  -> Gen a
+  -> Gen (Mat a)
+arbMatWith (Positive (Small r)) (Positive (Small c)) genA =
+    Mat r c <$> vectorOf r (vectorOf c genA)
 
 instance Arbitrary Matrix where
     arbitrary = fromMat <$> arbitrary