diff --git a/data-bword.cabal b/data-bword.cabal
--- a/data-bword.cabal
+++ b/data-bword.cabal
@@ -1,5 +1,5 @@
 Name: data-bword
-Version: 0.1
+Version: 0.1.0.1
 Category: Data
 Stability: experimental
 Synopsis: Extra operations on binary words of fixed length
diff --git a/src/Data/BinaryWord.hs b/src/Data/BinaryWord.hs
--- a/src/Data/BinaryWord.hs
+++ b/src/Data/BinaryWord.hs
@@ -20,7 +20,7 @@
 import Data.Word
 import Data.Bits (Bits(..))
 #if MIN_VERSION_base(4,7,0)
-import Data.Bits (FiniteBits)
+import Data.Bits (FiniteBits(..))
 #endif
 #if __GLASGOW_HASKELL__ >= 705
 import GHC.Prim (plusWord2#, timesWord2#)
@@ -109,6 +109,12 @@
           lo = fromIntegral p
           hi = fromIntegral (shiftR p 8)
   {-# INLINE unwrappedMul #-}
+#if MIN_VERSION_base(4,8,0)
+  leadingZeroes = countLeadingZeros
+  {-# INLINE leadingZeroes #-}
+  trailingZeroes = countTrailingZeros
+  {-# INLINE trailingZeroes #-}
+#else
   leadingZeroes w | w .&. 0xF0 == 0 = go4 4 w
                   | otherwise       = go4 0 (shiftR w 4)
     where go4 off w' | w' .&. 8 /= 0 = off
@@ -123,6 +129,7 @@
                      | w' .&. 4 /= 0 = off + 2
                      | w' .&. 8 /= 0 = off + 3
                      | otherwise     = off + 4
+#endif
   allZeroes = 0
   {-# INLINE allZeroes #-}
   allOnes = 0xFF
@@ -155,6 +162,12 @@
           lo = fromIntegral p
           hi = fromIntegral (shiftR p 16)
   {-# INLINE unwrappedMul #-}
+#if MIN_VERSION_base(4,8,0)
+  leadingZeroes = countLeadingZeros
+  {-# INLINE leadingZeroes #-}
+  trailingZeroes = countTrailingZeros
+  {-# INLINE trailingZeroes #-}
+#else
   leadingZeroes w | w .&. 0xFF00 == 0 = go8 8 w
                   | otherwise         = go8 0 (shiftR w 8)
     where
@@ -175,6 +188,7 @@
                  | w' .&. 4 /= 0    = off + 2
                  | w' .&. 8 /= 0    = off + 3
                  | otherwise        = off + 4
+#endif
   allZeroes = 0
   {-# INLINE allZeroes #-}
   allOnes = 0xFFFF
@@ -221,6 +235,12 @@
           hi = fromIntegral (shiftR p 32)
 #endif
   {-# INLINE unwrappedMul #-}
+#if MIN_VERSION_base(4,8,0)
+  leadingZeroes = countLeadingZeros
+  {-# INLINE leadingZeroes #-}
+  trailingZeroes = countTrailingZeros
+  {-# INLINE trailingZeroes #-}
+#else
   leadingZeroes w | w .&. 0xFFFF0000 == 0 = go16 16 w
                   | otherwise             = go16 0 (shiftR w 16)
     where
@@ -245,6 +265,7 @@
                   | w' .&. 4 /= 0      = off + 2
                   | w' .&. 8 /= 0      = off + 3
                   | otherwise          = off + 4
+#endif
   allZeroes = 0
   {-# INLINE allZeroes #-}
   allOnes = 0xFFFFFFFF
@@ -301,7 +322,13 @@
           (uHi1, uLo) = unwrappedAdd (fromIntegral p1) (fromIntegral p2)
           (uHi2, lo') = unwrappedAdd (fromIntegral (shiftR lo0 32)) uLo
 #endif
-#if WORD_SIZE_IN_BITS == 64
+#if MIN_VERSION_base(4,8,0)
+  leadingZeroes = countLeadingZeros
+  {-# INLINE leadingZeroes #-}
+  trailingZeroes = countTrailingZeros
+  {-# INLINE trailingZeroes #-}
+#else
+# if WORD_SIZE_IN_BITS == 64
   leadingZeroes w | w .&. 0xFFFFFFFF00000000 == 0 = go32 32 w
                   | otherwise                     = go32 0 (shiftR w 32)
     where
@@ -330,7 +357,7 @@
                   | w' .&. 4 /= 0          = off + 2
                   | w' .&. 8 /= 0          = off + 3
                   | otherwise              = off + 4
-#else
+# else
   leadingZeroes w | hiZeroes == 32 = 32 + leadingZeroes lo
                   | otherwise      = hiZeroes
     where lo = fromIntegral w ∷ Word32
@@ -341,6 +368,7 @@
     where lo = fromIntegral w ∷ Word32
           hi = fromIntegral (shiftR w 32) ∷ Word32
           loZeroes = trailingZeroes lo
+# endif
 #endif
   allZeroes = 0
   {-# INLINE allZeroes #-}
diff --git a/tests/Tests.hs b/tests/Tests.hs
--- a/tests/Tests.hs
+++ b/tests/Tests.hs
@@ -1,10 +1,14 @@
 {-# LANGUAGE UnicodeSyntax #-}
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
 
 import Test.Tasty (TestName, TestTree, defaultMain, localOption, testGroup)
 import Test.Tasty.QuickCheck hiding ((.&.))
 
 import Data.Bits (Bits(..))
+#if MIN_VERSION_base(4,7,0)
+import Data.Bits (FiniteBits(..))
+#endif
 import Data.Int
 import Data.Word
 import Data.BinaryWord
@@ -23,6 +27,11 @@
          , binWordGroup "Int64" (0 ∷ Int64)
          ]
 
+#if !MIN_VERSION_base(4,7,0)
+finiteBitSize ∷ Bits α ⇒ α → Int
+finiteBitSize = bitSize
+#endif
+
 sameType ∷ α → α → α
 sameType = const id
 
@@ -30,13 +39,41 @@
                 BinaryWord w) ⇒ TestName → w → TestTree
 binWordGroup n w = testGroup n
   [ testProperty "allZeroes" $ popCount (sameType w allZeroes) == 0
-  , testProperty "allOnes" $ popCount (sameType w allOnes) == bitSize w
+  , testProperty "allOnes" $ popCount (sameType w allOnes) == finiteBitSize w
+  , testProperty "msb" $
+      let bs = finiteBitSize w in
+        testBit (sameType w msb) (bs - 1) &&
+        all (not . testBit (sameType w msb)) [0 .. bs - 2]
+  , testProperty "lsb" $
+      let bs = finiteBitSize w in
+        testBit (sameType w lsb) 0 &&
+        all (not . testBit (sameType w lsb)) [1 .. bs - 1]
+  , testProperty "testMsb" $ \x →
+      testMsb (sameType w x) == testBit x (finiteBitSize x - 1)
+  , testProperty "testLsb" $ \x →
+      testLsb (sameType w x) == testBit x 0
+  , testProperty "leadingZeroes" $ \x →
+      let lz = leadingZeroes (sameType w x)
+          bs = finiteBitSize x in
+        if lz == 0
+        then testBit x (bs - 1)
+        else if lz == bs
+             then x == 0
+             else shiftR x (bs - lz) == 0 && testBit x (bs - lz - 1)
+  , testProperty "trailingZeroes" $ \x →
+      let tz = trailingZeroes (sameType w x)
+          bs = finiteBitSize x in
+        if tz == 0
+        then testBit x 0
+        else if tz == bs
+             then x == 0
+             else shiftL x (bs - tz) == 0 && testBit x tz
   , testProperty "unwrappedAdd" $ \w₁ w₂ →
       let (h, l) = unwrappedAdd (sameType w w₁) w₂ in
-        toInteger h * 2 ^ bitSize w + toInteger l ==
+        toInteger h * 2 ^ finiteBitSize w + toInteger l ==
           toInteger w₁ + toInteger w₂
   , testProperty "unwrappedMul" $ \w₁ w₂ →
       let (h, l) = unwrappedMul (sameType w w₁) w₂ in
-        toInteger h * 2 ^ bitSize w + toInteger l ==
+        toInteger h * 2 ^ finiteBitSize w + toInteger l ==
           toInteger w₁ * toInteger w₂
   ]