diff --git a/AC-Vector.cabal b/AC-Vector.cabal
--- a/AC-Vector.cabal
+++ b/AC-Vector.cabal
@@ -1,6 +1,6 @@
 Cabal-Version: >= 1.6
 Name:          AC-Vector
-Version:       2.3.1
+Version:       2.3.2
 Stability:     Experimental
 Synopsis:      Efficient geometric vectors and transformations.
 
@@ -13,9 +13,11 @@
   category, the package itself has no graphics facilities. It
   just contains data structures that are useful for graphics
   work.)
-
-  Added the @unions@ function. (More efficient than
-  @foldr1 union@.)
+  .
+  Changes:
+  .
+  * Fixed a stupid bug in @union@. Until now, the function could
+    sometimes return gibberish answers. Hopefully this is now fixed.
 
 Category:      Data, Math, Numerical, Graphics
 License:       BSD3
diff --git a/Data/BoundingBox/Range.hs b/Data/BoundingBox/Range.hs
--- a/Data/BoundingBox/Range.hs
+++ b/Data/BoundingBox/Range.hs
@@ -25,14 +25,15 @@
 
 -- | Take the union of two ranges. The resulting 'Range' contains all points that the original ranges contained, plus any points between them (if the original ranges don't overlap).
 union :: Range -> Range -> Range
-union (Range x00 x01) (Range x10 x11) = Range (min x00 x01) (max x01 x11)
+union (Range ll lh) (Range rl rh) = Range (min ll rl) (max lh rh)
 
 -- | Take the intersection of two ranges. If the ranges do not overlap, the intersection is empty, and 'Nothing' is returned. (This is a good way to check whether two ranges overlap or not.) Otherwise a new 'Range' is returned that contains only the points common to both ranges.
 isect :: Range -> Range -> Maybe Range
-isect (Range x00 x01) (Range x10 x11) =
-  if x00 < x10
-    then if x10 < x01 then Just (Range x10 (min x01 x11)) else Nothing
-    else if x00 < x11 then Just (Range x00 (min x01 x11)) else Nothing
+isect (Range ll lh) (Range rl rh) =
+  let
+    nl = max ll rl
+    nh = min lh rh
+  in  if nl > nh then Nothing else Just (Range nl nh)
 
 -- | Efficiently compute the union of a list of ranges.
 unions :: [Range] -> Range