diff --git a/Numeric/AD/Internal/Classes.hs b/Numeric/AD/Internal/Classes.hs
--- a/Numeric/AD/Internal/Classes.hs
+++ b/Numeric/AD/Internal/Classes.hs
@@ -199,7 +199,7 @@
         abs1          = lift1 abs signum1
         signum1       = lift1 signum (const zero)
         fromRational1 = lift . fromRational
-        (/!)          = lift2 (/) $ \x y -> (recip1 y, x)
+        (/!)          = lift2 (/) $ \x y -> (recip1 y, x *! negate1 (square1 y))
         recip1        = lift1 recip (negate1 . square1)
 
         pi1       = lift pi
diff --git a/ad.cabal b/ad.cabal
--- a/ad.cabal
+++ b/ad.cabal
@@ -1,5 +1,5 @@
 name:         ad
-version:      0.40
+version:      0.40.1
 license:      BSD3
 license-File: LICENSE
 copyright:    (c) Edward Kmett 2010,