diff --git a/Data/PrimitiveArray.hs b/Data/PrimitiveArray.hs
--- a/Data/PrimitiveArray.hs
+++ b/Data/PrimitiveArray.hs
@@ -151,7 +151,7 @@
 -- | Determines if an index is valid for a given immutable array.
 
 inBounds :: PrimArrayOps arr sh elm => arr sh elm -> sh -> Bool
-inBounds arr idx = let (lb,ub) = bounds arr in inShapeRange lb ub idx
+inBounds arr idx = let (lb,ub) = bounds arr in inShapeRange lb (ub `addDim` unitDim) idx
 {-# INLINE inBounds #-}
 
 -- | Returns all elements of an immutable array as a list.
diff --git a/Data/PrimitiveArray/Unboxed/VectorZero.hs b/Data/PrimitiveArray/Unboxed/VectorZero.hs
new file mode 100644
--- /dev/null
+++ b/Data/PrimitiveArray/Unboxed/VectorZero.hs
@@ -0,0 +1,71 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE FlexibleInstances #-}
+
+-- | Strict, unboxed arrays of primitive type. Uses unboxed vectors internally
+-- to provide tuple instances.
+
+module Data.PrimitiveArray.Unboxed.VectorZero where
+
+import Control.Monad
+import Data.Array.Repa.Index
+import Data.Array.Repa.Shape
+import Control.Exception (assert)
+import Data.Vector.Unboxed as VU hiding (forM_, length, zipWithM_)
+import Data.Vector.Unboxed.Mutable as VUM hiding (length)
+
+import Data.ExtShape
+import Data.PrimitiveArray
+
+
+
+-- | Monadic arrays of primitive type.
+
+data MArr0 s sh elm = MArr0 !sh !(MVector s elm)
+
+-- | Immutable arrays of primitive type.
+
+data Arr0 sh elm = Arr0 !sh !(Vector elm)
+
+
+
+type instance MutArray Arr0 = MArr0
+
+-- NOTE inLb, inUb is including bound, while exUb is excluding upper bound.
+-- Differentiates between largest included index, first excluded index.
+
+instance (Shape sh, ExtShape sh, VU.Unbox elm) => MPrimArrayOps MArr0 sh elm where
+  boundsM (MArr0 exUb _) = (zeroDim,exUb `subDim` unitDim)
+  fromListM inLb inUb xs = do
+    ma <- newM inLb inUb
+    let exUb = inUb `addDim` unitDim
+    let (MArr0 _ mba) = ma
+    zipWithM_ (\k x -> assert (length xs == size exUb) $ unsafeWrite mba k x) [0.. toIndex exUb inUb] xs
+    return ma
+  newM inLb inUb = let exUb = inUb `addDim` unitDim in
+    unless (inLb == zeroDim) (error "MArr0 lb/=zeroDim") >>
+    MArr0 exUb `liftM` new (size exUb)
+  newWithM inLb inUb def = do
+    let exUb = inUb `addDim` unitDim
+    ma <- newM inLb inUb
+    let (MArr0 _ mba) = ma
+    forM_ [0 .. toIndex exUb inUb] $ \k -> unsafeWrite mba k def
+    return ma
+  readM (MArr0 exUb mba) idx = assert (inShape exUb idx) $ unsafeRead mba (toIndex exUb idx)
+  writeM (MArr0 exUb mba) idx elm = assert (inShape exUb idx) $ unsafeWrite mba (toIndex exUb idx) elm
+  {-# INLINE boundsM #-}
+  {-# INLINE fromListM #-}
+  {-# INLINE newM #-}
+  {-# INLINE newWithM #-}
+  {-# INLINE readM #-}
+  {-# INLINE writeM #-}
+
+instance (Shape sh, ExtShape sh, VUM.Unbox elm) => PrimArrayOps Arr0 sh elm where
+  bounds (Arr0 exUb _) = (zeroDim,exUb `subDim` unitDim)
+  freeze (MArr0 exUb mba) = Arr0 exUb `liftM` unsafeFreeze mba
+  index (Arr0 exUb ba) idx = assert (inShape exUb idx) $ unsafeIndex ba (toIndex exUb idx)
+  {-# INLINE bounds #-}
+  {-# INLINE freeze #-}
+  {-# INLINE index #-}
+
diff --git a/PrimitiveArray.cabal b/PrimitiveArray.cabal
--- a/PrimitiveArray.cabal
+++ b/PrimitiveArray.cabal
@@ -1,5 +1,5 @@
 Name:           PrimitiveArray
-Version:        0.2.1.1
+Version:        0.2.2.0
 License:        BSD3
 License-file:   LICENSE
 Author:         Christian Hoener zu Siederdissen
@@ -25,6 +25,11 @@
                 always zero.
                 .
                 We have forked two repa modules: Shape and Index.
+                .
+                Unboxed vectors are available with implementations based on
+                "primitive" and "vector". For some reason, we loose 50%
+                performance with RNAfold if we use "vector" as the underlying
+                data type, while Nussinov78 does not suffer.
 
 Library
   Exposed-modules:
@@ -33,13 +38,14 @@
     Data.ExtShape
     Data.PrimitiveArray
     Data.PrimitiveArray.Unboxed.Zero
+    Data.PrimitiveArray.Unboxed.VectorZero
     Data.PrimitiveArray.Zero
   Build-depends:
     base >= 4 && <5,
     primitive >= 0.4,
     vector >= 0.9
   ghc-options:
-    -Odph
+    -O2
     -funbox-strict-fields