diff --git a/Dvda/Expr.hs b/Dvda/Expr.hs
--- a/Dvda/Expr.hs
+++ b/Dvda/Expr.hs
@@ -312,6 +312,7 @@
                             Just x' -> abs x'
 
   negate (EConst x) = EConst (negate x)
+  negate (ENum (Sub x y)) = y - x
   negate (ENum (FromInteger k)) = ENum (FromInteger (negate k))
   negate (EFractional (FromRational r)) = EFractional (FromRational (negate r))
   negate (ENum (Negate x)) = x
diff --git a/dvda.cabal b/dvda.cabal
--- a/dvda.cabal
+++ b/dvda.cabal
@@ -1,5 +1,5 @@
 Name:                dvda
-Version:             0.3.2
+Version:             0.3.2.1
 License:             BSD3
 License-file:        LICENSE
 Author:              Greg Horn