diff --git a/Crypto.cabal b/Crypto.cabal
--- a/Crypto.cabal
+++ b/Crypto.cabal
@@ -1,5 +1,5 @@
 Name:            Crypto
-Version:         4.2.0
+Version:         4.2.1
 License:         OtherLicense
 License-File:    ReadMe.tex
 Author:          Dominic Steinitz
@@ -46,9 +46,9 @@
                  Data.Digest.SHA512,
                  Data.LargeWord,
                  Data.HMAC
-        Build-Depends:  QuickCheck, HUnit
+        Build-Depends:  QuickCheck >= 2, HUnit
         if flag(small_base)
-            Build-Depends: base >= 3, array, random, pretty
+            Build-Depends: base >= 3, base < 5, array, random, pretty
         else
             Build-Depends: base < 3
         Ghc-options:     -fregs-graph
diff --git a/WordListTest.hs b/WordListTest.hs
--- a/WordListTest.hs
+++ b/WordListTest.hs
@@ -34,7 +34,6 @@
             mn = fromIntegral (minBound :: Word8)
         c <- choose (mx, mn)
         return $ fromIntegral c
-    coarbitrary a = error "Not implemented"
 
 instance Arbitrary Word32 where
     arbitrary = do
@@ -43,7 +42,6 @@
             mn = fromIntegral (minBound :: Word32)
         c <- choose (mx, mn)
         return $ fromIntegral c
-    coarbitrary a = error "Not implemented"
 
 instance Arbitrary Word64 where
     arbitrary = do
@@ -52,22 +50,18 @@
             mn = fromIntegral (minBound :: Word64)
         c <- choose (mx, mn)
         return $ fromIntegral c
-    coarbitrary a = error "Not implemented"
 
 instance Arbitrary Word128 where
         arbitrary = do
                 x <- vector (128 `div` 8) :: Gen [Word8]
                 return $ head $ listFromOctets x
-        coarbitrary x = error "Not implemented"
 
 instance Arbitrary Word192 where
         arbitrary = do
                 x <- vector (192 `div` 8) :: Gen [Word8]
                 return $ head $ listFromOctets x
-        coarbitrary x = error "Not implemented"
 
 instance Arbitrary Word256 where
         arbitrary = do
                 x <- vector (256 `div` 8) :: Gen [Word8]
                 return $ head $ listFromOctets x
-        coarbitrary x = error "Not implemented"