diff --git a/Data/Histogram/ST.hs b/Data/Histogram/ST.hs
--- a/Data/Histogram/ST.hs
+++ b/Data/Histogram/ST.hs
@@ -66,7 +66,7 @@
 -- | Put one monoidal element
 fillMonoid :: (PrimMonad m, Monoid a, U.Unbox a, Bin bin) => MHistogram (PrimState m) bin a -> (BinValue bin, a) -> m ()
 fillMonoid (MHistogram bin uo arr) !(x,m)
-    | i < 0              = MU.unsafeWrite uo  1 . flip mappend m =<< MU.unsafeRead uo  0
+    | i < 0              = MU.unsafeWrite uo  0 . flip mappend m =<< MU.unsafeRead uo  0
     | i >= MU.length arr = MU.unsafeWrite uo  1 . flip mappend m =<< MU.unsafeRead uo  1
     | otherwise          = MU.unsafeWrite arr i . flip mappend m =<< MU.unsafeRead arr i
     where 
diff --git a/histogram-fill.cabal b/histogram-fill.cabal
--- a/histogram-fill.cabal
+++ b/histogram-fill.cabal
@@ -1,5 +1,5 @@
 Name:           histogram-fill
-Version:        0.3
+Version:        0.3.0.1
 Cabal-Version:  >= 1.6
 License:        BSD3
 License-File:   LICENSE