diff --git a/Data/Number/Natural.hs b/Data/Number/Natural.hs
--- a/Data/Number/Natural.hs
+++ b/Data/Number/Natural.hs
@@ -66,12 +66,17 @@
     pred (S a) = a
     toEnum = fromIntegral
     fromEnum = fromIntegral
-    enumFromThenTo from thn to = go from (to `maybeSubtract` from) where
+    enumFromThenTo from thn to | from <= thn = go from (to `maybeSubtract` from) where
       go from Nothing      = []
-      go from (Just count) = from:go (thn + from) (count `maybeSubtract` thn)
-    enumFrom a       = enumFromThenTo a 1 infinity
+      go from (Just count) = from:go (step + from) (count `maybeSubtract` step)
+      step = thn - from
+    enumFromThenTo from thn to | otherwise = go (from + step) where
+      go from | from >= to + step = let next = from - step in next:go next
+              | otherwise         = []
+      step = from - thn
+    enumFrom a       = enumFromThenTo a (S a) infinity
     enumFromThen a b = enumFromThenTo a b infinity
-    enumFromTo a c   = enumFromThenTo a 1 c
+    enumFromTo a c   = enumFromThenTo a (S a) c
 
 -- | The infinite natural number.
 infinity :: Natural
diff --git a/numbers.cabal b/numbers.cabal
--- a/numbers.cabal
+++ b/numbers.cabal
@@ -1,5 +1,5 @@
 Name:		numbers
-Version:	2009.5.20.1
+Version:	2009.5.28.1
 License:	BSD3
 Author:		Lennart Augustsson
 Maintainer:	Lennart Augustsson