diff --git a/hstatistics.cabal b/hstatistics.cabal
--- a/hstatistics.cabal
+++ b/hstatistics.cabal
@@ -1,5 +1,5 @@
 Name:               hstatistics
-Version:            0.2.0.1
+Version:            0.2.0.2
 License:            GPL
 License-file:       LICENSE
 Copyright:          (c) A.V.H. McPhail 2010
diff --git a/lib/Numeric/Statistics/Shannon.hs b/lib/Numeric/Statistics/Shannon.hs
--- a/lib/Numeric/Statistics/Shannon.hs
+++ b/lib/Numeric/Statistics/Shannon.hs
@@ -29,10 +29,13 @@
 
 sum x = dot x (constant  1 (dim x))
 
+prob p y = let Just y' = find p y 
+           in getBin p y'
+
 -- | the entropy \sum p_i l\ln{p_i} of a sequence
 entropy :: Histogram             -- the underlying distribution
-        -> Vector Double         -- the sequence
+        -> Vector Double         -- the sequence (expected to fall within bounds of Histogram)
         -> Double                -- the entropy
-entropy p x = let ps = mapVector (\y -> let Just y' = find p y in getBin p y') x
+entropy p x = let ps = mapVector (prob p) x
               in sum (ps * log ps)