diff --git a/LATS.cabal b/LATS.cabal
--- a/LATS.cabal
+++ b/LATS.cabal
@@ -1,5 +1,5 @@
 name:                LATS
-version:             0.4.1
+version:             0.4.2
 synopsis:            Linear Algebra on Typed Spaces
 description:         Please see README.org
 homepage:            http://github.com/guaraqe/lats#readme
@@ -28,6 +28,8 @@
                      , hmatrix >= 0.17 && < 0.18
                      , semigroups >= 0.18 && < 0.19
                      , vector >= 0.11 && < 0.12
+
+  extra-libraries:     openblas
 
   default-language:    Haskell2010
 
diff --git a/src/LinearAlgebra/TypedSpaces/Classes.hs b/src/LinearAlgebra/TypedSpaces/Classes.hs
--- a/src/LinearAlgebra/TypedSpaces/Classes.hs
+++ b/src/LinearAlgebra/TypedSpaces/Classes.hs
@@ -10,7 +10,7 @@
        , IsList       (..)
        , module CC ) where
 
-import GHC.Exts (IsList (..))
+import GHC.Exts (IsList (..), Constraint)
 import Control.ConstraintClasses as CC
 
 ----------------------------------------------------------------------
@@ -35,7 +35,9 @@
 ----------------------------------------------------------------------
 
 class CFunctor f => CIndexed f i | f -> i where
+  type CInd f a :: Constraint
+  type CInd f a = ()
 
-  (!) :: CFun f a => f a -> i -> a
+  (!) :: (CFun f a, CInd f a) => f a -> i -> a
 
 ----------------------------------------------------------------------
diff --git a/src/LinearAlgebra/TypedSpaces/Matrix.hs b/src/LinearAlgebra/TypedSpaces/Matrix.hs
--- a/src/LinearAlgebra/TypedSpaces/Matrix.hs
+++ b/src/LinearAlgebra/TypedSpaces/Matrix.hs
@@ -37,18 +37,21 @@
 newtype Matrix i j a = Matrix { matrix :: L.Matrix a }
   deriving (Show)
 
-instance (Isomorphism Int i, Isomorphism Int j)
-      => CIndexed (Matrix i j) (i,j) where
-
-  (Matrix v) ! (m,n) = v `L.atIndex` (bw m, bw n)
-
 instance CFunctor (Matrix i j) where
 
-  type CFun (Matrix i j) a = ( L.Container L.Matrix a
+  type CFun (Matrix i j) a = ( L.Container L.Vector a
                              , L.Storable a
                              , Num a )
 
   cmap f (Matrix m) = Matrix (L.cmap f m)
+
+
+instance (Isomorphism Int i, Isomorphism Int j)
+      => CIndexed (Matrix i j) (i,j) where
+
+  type CInd (Matrix i j) a = (L.Container L.Vector a)
+
+  (Matrix v) ! (m,n) = v `L.atIndex` (bw m, bw n)
 
 ----------------------------------------------------------------------