diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,16 @@
 # ChangeLog
 
+## 0.3.1
+
+* Fix to derivation of primitive vectors, only relevant when built with
+  primitive-0.6.2.0 or later
+
+* Removes INLINE pragmas on the generic default methods.  This
+  dramatically improves compilation time on recent GHC versions.
+  See [#91](https://github.com/fpco/store/issues/91).
+
+* Adds `instance Contravariant Size`
+
 ## 0.3
 
 * Uses store-core-0.3.*, which has support for alignment sensitive
diff --git a/src/Data/Store/Impl.hs b/src/Data/Store/Impl.hs
--- a/src/Data/Store/Impl.hs
+++ b/src/Data/Store/Impl.hs
@@ -22,6 +22,7 @@
 import           Control.Exception (try)
 import           Control.Monad
 import qualified Data.ByteString as BS
+import           Data.Functor.Contravariant (Contravariant(..))
 import           Data.Proxy
 import           Data.Store.Core
 import           Data.Typeable (Typeable, typeRep)
@@ -64,16 +65,18 @@
 
     default size :: (Generic a, GStoreSize (Rep a)) => Size a
     size = genericSize
-    {-# INLINE size #-}
 
     default poke :: (Generic a, GStorePoke (Rep a)) => a -> Poke ()
     poke = genericPoke
-    {-# INLINE poke #-}
 
     default peek :: (Generic a , GStorePeek (Rep a)) => Peek a
     peek = genericPeek
-    {-# INLINE peek #-}
 
+    -- NB: Do not INLINE the default implementations of size, poke, or peek!
+    -- Doing so can lead to enormous memory blowup (a maximum residency of
+    -- 5.17 GB with GHC 8.0.2 has been observed). For more information, please
+    -- read issue #91.
+
 ------------------------------------------------------------------------
 -- Utilities for encoding / decoding strict ByteStrings
 
@@ -118,6 +121,11 @@
     | ConstSize !Int
     deriving Typeable
 
+instance Contravariant Size where
+  contramap f sz = case sz of
+    ConstSize n -> ConstSize n
+    VarSize g -> VarSize (\x -> g (f x))
+
 -- | Get the number of bytes needed to store the given value. See
 -- 'size'.
 getSize :: Store a => a -> Int
@@ -131,13 +139,6 @@
 getSizeWith (ConstSize n) _ = n
 {-# INLINE getSizeWith #-}
 
--- | This allows for changing the type used as an input when the 'Size'
--- is 'VarSize'.
-contramapSize :: (a -> b) -> Size b -> Size a
-contramapSize f (VarSize g) = VarSize (g . f)
-contramapSize _ (ConstSize n) = ConstSize n
-{-# INLINE contramapSize #-}
-
 -- | Create an aggregate 'Size' by providing functions to split the
 -- input into two pieces.
 --
@@ -186,7 +187,7 @@
 -- Generics
 
 genericSize :: (Generic a, GStoreSize (Rep a)) => Size a
-genericSize = contramapSize from gsize
+genericSize = contramap from gsize
 {-# INLINE genericSize #-}
 
 genericPoke :: (Generic a, GStorePoke (Rep a)) => a -> Poke ()
@@ -211,7 +212,7 @@
 class GStorePeek f where gpeek :: Peek (f a)
 
 instance GStoreSize f => GStoreSize (M1 i c f) where
-    gsize = contramapSize unM1 gsize
+    gsize = contramap unM1 gsize
     {-# INLINE gsize #-}
 instance GStorePoke f => GStorePoke (M1 i c f) where
     gpoke = gpoke . unM1
@@ -221,7 +222,7 @@
     {-# INLINE gpeek #-}
 
 instance Store a => GStoreSize (K1 i a) where
-    gsize = contramapSize unK1 size
+    gsize = contramap unK1 size
     {-# INLINE gsize #-}
 instance Store a => GStorePoke (K1 i a) where
     gpoke = poke . unK1
diff --git a/src/Data/Store/Internal.hs b/src/Data/Store/Internal.hs
--- a/src/Data/Store/Internal.hs
+++ b/src/Data/Store/Internal.hs
@@ -39,7 +39,7 @@
     -- ** Size type
     , Size(..)
     , getSize, getSizeWith
-    , contramapSize, combineSize, combineSizeWith, addSize
+    , combineSize, combineSizeWith, addSize
     -- ** Store instances in terms of IsSequence
     , sizeSequence, pokeSequence, peekSequence
     -- ** Store instances in terms of IsSet
@@ -76,6 +76,7 @@
 import           Data.Data (Data)
 import           Data.Fixed (Fixed (..), Pico)
 import           Data.Foldable (forM_, foldl')
+import           Data.Functor.Contravariant
 import           Data.HashMap.Strict (HashMap)
 import           Data.HashSet (HashSet)
 import           Data.Hashable (Hashable)
@@ -620,7 +621,7 @@
 -- instance Store GHC.Fingerprint.Types.Fingerprint where
 
 instance Store (Fixed a) where
-    size = contramapSize (\(MkFixed x) -> x) (size :: Size Integer)
+    size = contramap (\(MkFixed x) -> x) (size :: Size Integer)
     poke (MkFixed x) = poke x
     peek = MkFixed <$> peek
     {-# INLINE size #-}
@@ -649,7 +650,7 @@
     {-# INLINE poke #-}
 
 instance Store Time.Day where
-    size = contramapSize Time.toModifiedJulianDay (size :: Size Integer)
+    size = contramap Time.toModifiedJulianDay (size :: Size Integer)
     poke = poke . Time.toModifiedJulianDay
     peek = Time.ModifiedJulianDay <$> peek
     {-# INLINE size #-}
@@ -657,7 +658,7 @@
     {-# INLINE poke #-}
 
 instance Store Time.DiffTime where
-    size = contramapSize (realToFrac :: Time.DiffTime -> Pico) (size :: Size Pico)
+    size = contramap (realToFrac :: Time.DiffTime -> Pico) (size :: Size Pico)
     poke = (poke :: Pico -> Poke ()) . realToFrac
     peek = Time.picosecondsToDiffTime <$> peek
     {-# INLINE size #-}
diff --git a/src/Data/Store/Streaming.hs b/src/Data/Store/Streaming.hs
--- a/src/Data/Store/Streaming.hs
+++ b/src/Data/Store/Streaming.hs
@@ -115,22 +115,27 @@
         Right ptr -> decodeFromPtr ptr n
 {-# INLINE peekSized #-}
 
--- | Decode a header (magic number and 'SizeTag') from a 'ByteBuffer'.
-peekMessageHeader :: MonadIO m => FillByteBuffer i m -> ByteBuffer -> PeekMessage i m SizeTag
-peekMessageHeader fill bb = go
-  where
-    go = do
-      messageMagic' <- peekSized fill bb magicLength
-      unless (messageMagic == messageMagic') $
-        liftIO . throwIO $ PeekException 0 . T.pack $ "Wrong message magic, " ++ show messageMagic'
-      peekSized fill bb sizeTagLength
-{-# INLINE peekMessageHeader #-}
+-- | Read and check the magic number from a 'ByteBuffer'
+peekMessageMagic :: MonadIO m => FillByteBuffer i m -> ByteBuffer -> PeekMessage i m ()
+peekMessageMagic fill bb =
+    peekSized fill bb magicLength >>= \case
+      mm | mm == messageMagic -> return ()
+      mm -> liftIO . throwIO $ PeekException 0 . T.pack $
+          "Wrong message magic, " ++ show mm
+{-# INLINE peekMessageMagic #-}
 
+-- | Decode a 'SizeTag' from a 'ByteBuffer'.
+peekMessageSizeTag :: MonadIO m => FillByteBuffer i m -> ByteBuffer -> PeekMessage i m SizeTag
+peekMessageSizeTag fill bb = peekSized fill bb sizeTagLength
+{-# INLINE peekMessageSizeTag #-}
+
 -- | Decode some object from a 'ByteBuffer', by first reading its
 -- header, and then the actual data.
 peekMessage :: (MonadIO m, Store a) => FillByteBuffer i m -> ByteBuffer -> PeekMessage i m (Message a)
 peekMessage fill bb =
-  fmap Message (peekSized fill bb =<< peekMessageHeader fill bb)
+  fmap Message $ do
+    peekMessageMagic fill bb
+    peekMessageSizeTag fill bb >>= peekSized fill bb
 {-# INLINE peekMessage #-}
 
 -- | Decode a 'Message' from a 'ByteBuffer' and an action that can get
@@ -141,15 +146,25 @@
 -- 'Nothing'.  If there is some data available, but not enough to
 -- decode the whole 'Message', a 'PeekException' will be thrown.
 decodeMessage :: (Store a, MonadIO m) => FillByteBuffer i m -> ByteBuffer -> m (Maybe i) -> m (Maybe (Message a))
-decodeMessage fill bb getInp = do
-  mbRes <- runMaybeT (iterTM (\consumeInp -> consumeInp =<< MaybeT getInp) (peekMessage fill bb))
-  case mbRes of
-    Just x -> return (Just x)
+decodeMessage fill bb getInp =
+  maybeDecode (peekMessageMagic fill bb) >>= \case
+    Just () -> maybeDecode (peekMessageSizeTag fill bb >>= peekSized fill bb) >>= \case
+      Just x -> return (Just (Message x))
+      Nothing -> do
+        -- We have already read the message magic, so a failure to
+        -- read the whole message means we have an incomplete message.
+        available <- BB.availableBytes bb
+        liftIO $ throwIO $ PeekException available $ T.pack
+          "Data.Store.Streaming.decodeMessage: could not get enough bytes to decode message"
     Nothing -> do
       available <- BB.availableBytes bb
-      unless (available == 0) $ liftIO $ throwIO $ PeekException available $ T.pack $
+      -- At this point, we have not consumed anything yet, so if bb is
+      -- empty, there simply was no message to read.
+      unless (available == 0) $ liftIO $ throwIO $ PeekException available $ T.pack
         "Data.Store.Streaming.decodeMessage: could not get enough bytes to decode message"
       return Nothing
+  where
+    maybeDecode m = runMaybeT (iterTM (\consumeInp -> consumeInp =<< MaybeT getInp) m)
 {-# INLINE decodeMessage #-}
 
 -- | Decode some 'Message' from a 'ByteBuffer', by first reading its
diff --git a/src/Data/Store/TH/Internal.hs b/src/Data/Store/TH/Internal.hs
--- a/src/Data/Store/TH/Internal.hs
+++ b/src/Data/Store/TH/Internal.hs
@@ -290,7 +290,7 @@
             `M.difference`
             stores
     forM (M.toList primInsts) $ \primInst -> case primInst of
-        ([instTy], TypeclassInstance cs ty _) -> do
+        ([_], TypeclassInstance cs ty _) -> do
             let argTy = head (tail (unAppsT ty))
             sizeExpr <- [|
                 VarSize $ \x ->
@@ -309,7 +309,7 @@
                 poke len
                 pokeFromByteArray array (offset * sz) (len * sz)
                 |]
-            return $ makeStoreInstance cs instTy sizeExpr peekExpr pokeExpr
+            return $ makeStoreInstance cs (AppT (ConT ''PV.Vector) argTy) sizeExpr peekExpr pokeExpr
         _ -> fail "Invariant violated in derivemanyStorePrimVector"
 
 
diff --git a/src/Data/Store/TypeHash/Internal.hs b/src/Data/Store/TypeHash/Internal.hs
--- a/src/Data/Store/TypeHash/Internal.hs
+++ b/src/Data/Store/TypeHash/Internal.hs
@@ -16,6 +16,7 @@
 import qualified Data.ByteString as BS
 import           Data.Char (isUpper, isLower)
 import           Data.Data (Data)
+import           Data.Functor.Contravariant
 import           Data.Generics (listify)
 import           Data.List (sortBy)
 import           Data.Monoid ((<>))
@@ -40,7 +41,7 @@
 instance NFData a => NFData (Tagged a)
 
 instance (Store a, HasTypeHash a) => Store (Tagged a) where
-    size = addSize 20 (contramapSize unTagged size)
+    size = addSize 20 (contramap unTagged size)
     peek = do
         tag <- peek
         let expected = typeHash (Proxy :: Proxy a)
diff --git a/store.cabal b/store.cabal
--- a/store.cabal
+++ b/store.cabal
@@ -1,9 +1,9 @@
--- This file has been generated from package.yaml by hpack version 0.14.1.
+-- This file has been generated from package.yaml by hpack version 0.17.0.
 --
 -- see: https://github.com/sol/hpack
 
 name:           store
-version:        0.3
+version:        0.3.1
 synopsis:       Fast binary serialization
 category:       Serialization, Data
 homepage:       https://github.com/fpco/store#readme
@@ -78,6 +78,7 @@
     , network >=2.6.0.2
     , streaming-commons >=0.1.10.0
     , async >=2.0.2
+    , contravariant >=1.3
   exposed-modules:
       Data.Store
       Data.Store.Internal
@@ -142,6 +143,7 @@
     , network >=2.6.0.2
     , streaming-commons >=0.1.10.0
     , async >=2.0.2
+    , contravariant >=1.3
     , store
   other-modules:
       Data.Store.StreamingSpec
@@ -199,18 +201,13 @@
     , network >=2.6.0.2
     , streaming-commons >=0.1.10.0
     , async >=2.0.2
+    , contravariant >=1.3
     , store
     , weigh
     , criterion
     , cereal
     , cereal-vector
     , vector-binary-instances
-  other-modules:
-      Data.Store.StreamingSpec
-      Data.StoreSpec
-      Data.StoreSpec.TH
-      Spec
-      System.IO.ByteBufferSpec
   default-language: Haskell2010
 
 benchmark store-bench
@@ -262,6 +259,7 @@
     , network >=2.6.0.2
     , streaming-commons >=0.1.10.0
     , async >=2.0.2
+    , contravariant >=1.3
     , criterion
     , store
   if flag(comparison-bench)
diff --git a/test/Data/Store/StreamingSpec.hs b/test/Data/Store/StreamingSpec.hs
--- a/test/Data/Store/StreamingSpec.hs
+++ b/test/Data/Store/StreamingSpec.hs
@@ -50,7 +50,6 @@
     describe "ByteString" $ do
       it "Throws an Exception on incomplete messages." decodeIncomplete
       it "Throws an Exception on messages that are shorter than indicated." decodeTooShort
-      it "Throws an Exception on messages that are longer than indicated." decodeTooLong
 #ifndef mingw32_HOST_OS
     describe "Socket" $ do
       it "Decodes data trickling through a socket." $ property decodeTricklingMessageFd
@@ -196,26 +195,14 @@
   let bs = encodeMessage (Message (42 :: Integer))
   in BS.take (BS.length bs - 1) bs
 
-decodeTooLong :: IO ()
-decodeTooLong = BB.with Nothing $ \bb -> do
-    BB.copyByteString bb (encodeMessageTooLong . Message $ (1 :: Int))
-    (decodeMessageBS bb (return Nothing) :: IO (Maybe (Message Int)))
-        `shouldThrow` \PeekException{} -> True
-
 decodeTooShort :: IO ()
 decodeTooShort = BB.with Nothing $ \bb -> do
     BB.copyByteString bb (encodeMessageTooShort . Message $ (1 :: Int))
     (decodeMessageBS bb (return Nothing) :: IO (Maybe (Message Int)))
         `shouldThrow` \PeekException{} -> True
 
-encodeMessageTooLong :: Store a => Message a -> BS.ByteString
-encodeMessageTooLong (Message x) =
-    let l = 8 + getSize x
-        totalLength = 8 + l
-    in unsafeEncodeWith (poke l >> poke x >> poke (0::Int64)) totalLength
-
-encodeMessageTooShort :: Store a => Message a -> BS.ByteString
-encodeMessageTooShort (Message _x) =
-    let l = 0
-        totalLength = 8 + l
-    in unsafeEncodeWith (poke l) totalLength
+encodeMessageTooShort :: Message Int -> BS.ByteString
+encodeMessageTooShort msg =
+    BS.take (BS.length encoded - (getSize (0 :: Int))) encoded
+  where
+    encoded = encodeMessage msg
diff --git a/test/Data/StoreSpec.hs b/test/Data/StoreSpec.hs
--- a/test/Data/StoreSpec.hs
+++ b/test/Data/StoreSpec.hs
@@ -392,6 +392,10 @@
                             , BS.drop (sizeOf (10 :: Int)) bs
                             ]
         evaluate (decodeEx bs' :: BS.ByteString) `shouldThrow` isTooManyBytesException
+    it "Handles unaligned access" $ do
+        assertRoundtrip verbose (250 :: Word8, 40918 :: Word16, 120471416 :: Word32)
+        assertRoundtrip verbose (250 :: Word8, 10.1 :: Float, 8697.65 :: Double)
+        (return () :: IO ())
 
 isPokeException :: Test.Hspec.Selector PokeException
 isPokeException = const True