diff --git a/changelog b/changelog
--- a/changelog
+++ b/changelog
@@ -1,5 +1,10 @@
 -*-change-log-*-
 
+v0.2.4.0 TDB
+
+v0.2.3.1 December 2016
+ * Merge fix for storable instance
+
 v0.2.3.0 December 2016
  * Add Contour Tracing (Vision.Image.Contour)
  * Add pointer to friday-juicypixels
diff --git a/friday.cabal b/friday.cabal
--- a/friday.cabal
+++ b/friday.cabal
@@ -2,7 +2,7 @@
 --                      +-+------- breaking API changes
 --                      | | +----- non-breaking API additions
 --                      | | | +--- code changes with no API change
-version:                0.2.3.0
+version:                0.2.3.1
 synopsis:               A functional image processing library for Haskell.
 homepage:               https://github.com/RaphaelJ/friday
 license:                LGPL-3
@@ -65,7 +65,7 @@
                         Vision.Image.RGBA
                         Vision.Image.RGBA.Specialize
                         Vision.Image.RGBA.Type
-                        Vision.Image.RGB 
+                        Vision.Image.RGB
                         Vision.Image.RGB.Specialize
                         Vision.Image.RGB.Type
                         Vision.Image.Threshold
@@ -93,6 +93,8 @@
     main-is:            Test.hs
     other-modules:      Test.Vision.Histogram
                         Test.Vision.Image
+                        Test.Vision.Primitive
+                        Test.Utils
     ghc-options:        -Wall -O2 -rtsopts
     hs-source-dirs:     test/
     default-language:   Haskell2010
diff --git a/src/Vision/Primitive/Shape.hs b/src/Vision/Primitive/Shape.hs
--- a/src/Vision/Primitive/Shape.hs
+++ b/src/Vision/Primitive/Shape.hs
@@ -222,12 +222,12 @@
 
     peek !ptr = do
         let !ptr' = castPtr ptr
-        (:.) <$> peek (castPtr $! ptr' `plusPtr` 1) <*> peek ptr'
+        (:.) <$> peek (castPtr $! ptr' `plusPtr` sizeOf (undefined :: Int)) <*> peek ptr'
     {-# INLINE peek #-}
 
     poke !ptr (sh :. n) = do
         let !ptr' = castPtr ptr
-        poke (castPtr $! ptr' `plusPtr` 1) sh >> poke ptr' n
+        poke (castPtr $! ptr' `plusPtr` sizeOf n) sh >> poke ptr' n
     {-# INLINE poke #-}
 
 -- | Helper for index construction.
diff --git a/test/Test.hs b/test/Test.hs
--- a/test/Test.hs
+++ b/test/Test.hs
@@ -2,9 +2,11 @@
 
 import qualified Test.Vision.Image as I
 import qualified Test.Vision.Histogram as H
+import qualified Test.Vision.Primitive as P
 
 main :: IO ()
 main = defaultMain [
       testGroup "Images"     I.tests
     , testGroup "Histograms" H.tests
+    , testGroup "Primitives" P.tests
     ]
diff --git a/test/Test/Utils.hs b/test/Test/Utils.hs
new file mode 100644
--- /dev/null
+++ b/test/Test/Utils.hs
@@ -0,0 +1,15 @@
+
+module Test.Utils
+( propStorableRoundtrip
+) where
+
+import Foreign (Storable, with, peek)
+
+import Test.QuickCheck (Property)
+import Test.QuickCheck.Monadic (monadicIO, run, assert)
+
+propStorableRoundtrip :: (Eq a, Storable a) => a -> Property
+propStorableRoundtrip a = monadicIO $ do
+    a' <- run . with a $ peek
+    assert $ a' == a
+
diff --git a/test/Test/Vision/Image.hs b/test/Test/Vision/Image.hs
--- a/test/Test/Vision/Image.hs
+++ b/test/Test/Vision/Image.hs
@@ -14,12 +14,13 @@
 import Data.Vector.Storable (Storable, replicateM)
 import Test.Framework (Test, testGroup)
 import Test.Framework.Providers.QuickCheck2 (testProperty)
-import Test.QuickCheck (Arbitrary (..), choose)
+import Test.QuickCheck (Arbitrary (..), choose, Property)
+import Test.Utils (propStorableRoundtrip)
 
 import Vision.Image (
       MaskedImage (..), Image (..), Interpolable, FromFunction (..)
     , ImageChannel, Manifest (..), Delayed (..)
-    , Grey, GreyPixel (..), HSVPixel
+    , Grey, GreyPixel (..), HSVPixel (..)
     , RGBA, RGBAPixel (..), RGBADelayed
     , RGB, RGBPixel (..), InterpolMethod (..)
     , convert, resize, horizontalFlip, verticalFlip
@@ -46,6 +47,9 @@
 instance Arbitrary RGBPixel where
     arbitrary = RGBPixel <$> arbitrary <*> arbitrary <*> arbitrary
 
+instance Arbitrary HSVPixel where
+    arbitrary = HSVPixel <$> arbitrary <*> arbitrary <*> arbitrary
+
 tests :: [Test]
 tests = [
       testGroup "Conversions identities" [
@@ -66,6 +70,11 @@
           testProperty "Grey" (propVerticalFlip :: Grey -> Bool)
         , testProperty "RGBA" (propVerticalFlip :: RGBA -> Bool)
         , testProperty "RGB"  (propVerticalFlip :: RGB  -> Bool)
+        ]
+    , testGroup "Storable can roundtrip" [
+          testProperty "HSVPixel" $ (propStorableRoundtrip :: HSVPixel -> Property)
+        , testProperty "RGBPixel" $ (propStorableRoundtrip :: RGBPixel -> Property)
+        , testProperty "RGBAPixel" $ (propStorableRoundtrip :: RGBAPixel -> Property)
         ]
     ]
 
diff --git a/test/Test/Vision/Primitive.hs b/test/Test/Vision/Primitive.hs
new file mode 100644
--- /dev/null
+++ b/test/Test/Vision/Primitive.hs
@@ -0,0 +1,41 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE TypeOperators #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Test.Vision.Primitive
+( tests
+) where
+
+#if __GLASGOW_HASKELL__ < 710
+import Control.Applicative ((<*>), (<$>))
+#endif
+
+import Test.Framework (Test, testGroup)
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+import Test.QuickCheck (Arbitrary (..), Property)
+import Test.Utils (propStorableRoundtrip)
+
+import Vision.Primitive
+
+instance Arbitrary Z where
+    arbitrary = return Z
+
+instance (Arbitrary t, Arbitrary h) => Arbitrary (t :. h) where
+    arbitrary = (:.) <$> arbitrary <*> arbitrary
+
+tests :: [Test]
+tests =
+    [ testGroup "Storable can roundtrip"
+        [ testProperty "DIM0" $ (propStorableRoundtrip :: DIM0 -> Property)
+        , testProperty "DIM1" $ (propStorableRoundtrip :: DIM1 -> Property)
+        , testProperty "DIM2" $ (propStorableRoundtrip :: DIM2 -> Property)
+        , testProperty "DIM3" $ (propStorableRoundtrip :: DIM3 -> Property)
+        , testProperty "DIM4" $ (propStorableRoundtrip :: DIM4 -> Property)
+        , testProperty "DIM5" $ (propStorableRoundtrip :: DIM5 -> Property)
+        , testProperty "DIM6" $ (propStorableRoundtrip :: DIM6 -> Property)
+        , testProperty "DIM7" $ (propStorableRoundtrip :: DIM7 -> Property)
+        , testProperty "DIM8" $ (propStorableRoundtrip :: DIM8 -> Property)
+        , testProperty "DIM9" $ (propStorableRoundtrip :: DIM9 -> Property)
+        ]
+    ]
+