diff --git a/chatter.cabal b/chatter.cabal
--- a/chatter.cabal
+++ b/chatter.cabal
@@ -1,5 +1,5 @@
 name:                chatter
-version:             0.0.0.3
+version:             0.0.0.4
 synopsis:            A library of simple NLP algorithms.
 description:         chatter is a collection of simple Natural Language
                      Processing algorithms.
@@ -143,6 +143,8 @@
                      NLP.Similarity.VectorSimTests
                      NLP.POSTests
                      NLP.POS.UnambiguousTaggerTests
+                     NLP.TypesTests
+                     Data.DefaultMapTests
                      Corpora
                      TestUtils
 
diff --git a/src/Data/DefaultMap.hs b/src/Data/DefaultMap.hs
--- a/src/Data/DefaultMap.hs
+++ b/src/Data/DefaultMap.hs
@@ -3,6 +3,7 @@
 
 import Data.Map (Map)
 import qualified Data.Map as Map
+import Data.Serialize
 
 -- | Defaulting Map; a Map that returns a default value when queried
 -- for a key that does not exist.
@@ -37,3 +38,8 @@
 -- standard `Data.Map.foldl`
 foldl :: (a -> b -> a) -> a -> DefaultMap k b -> a
 foldl fn acc m = Map.foldl fn acc (defMap m)
+
+-- | Serialize instance
+instance (Ord k, Serialize k, Serialize v) => Serialize (DefaultMap k v) where
+  get   = fmap (uncurry DefMap) (getTwoOf get get)
+  put m = (putTwoOf put put) (defDefault m, defMap m)
diff --git a/src/NLP/POS.hs b/src/NLP/POS.hs
--- a/src/NLP/POS.hs
+++ b/src/NLP/POS.hs
@@ -51,7 +51,7 @@
 
 import NLP.Corpora.Parsing (readPOS)
 
-import NLP.Types (TaggedSentence, Tag(..)
+import NLP.Types (TaggedSentence, Tag(..), Sentence
                  , POSTagger(..), tagUNK, stripTags)
 
 import qualified NLP.POS.LiteralTagger as LT
@@ -125,10 +125,14 @@
 tag :: POSTagger -> Text -> [TaggedSentence]
 tag p txt = let sentences = (posSplitter p) txt
                 tokens    = map (posTokenizer p) sentences
-                priority  = (posTagger p) tokens
-            in case posBackoff p of
-                 Nothing  -> priority
-                 Just tgr -> combine priority (tag tgr txt)
+            in tagTokens p tokens
+
+tagTokens :: POSTagger -> [Sentence] -> [TaggedSentence]
+tagTokens p tokens = let priority = (posTagger p) tokens
+                     in case posBackoff p of
+                          Nothing  -> priority
+                          Just tgr -> combine priority (tagTokens tgr tokens)
+
 
 -- | Combine the results of POS taggers, using the second param to
 -- fill in 'tagUNK' entries, where possible.
diff --git a/src/NLP/Types.hs b/src/NLP/Types.hs
--- a/src/NLP/Types.hs
+++ b/src/NLP/Types.hs
@@ -7,7 +7,7 @@
 import Data.ByteString (ByteString)
 import Data.Map (Map)
 import qualified Data.Map as Map
-import Data.Serialize (Serialize, put, get)
+import Data.Serialize (Serialize, put, get, getTwoOf, putTwoOf)
 import Data.Set (Set)
 import qualified Data.Set as Set
 import Data.Text (Text)
@@ -98,6 +98,10 @@
                      , corpTermCounts :: Map Text Int
                      -- ^ A count of the number of documents each term occurred in.
                      } deriving (Read, Show, Eq, Ord)
+
+instance Serialize Corpus where
+  get   = fmap (uncurry Corpus) (getTwoOf get get)
+  put c = (putTwoOf put put) (corpLength c, corpTermCounts c)
 
 -- | Get the number of documents that a term occurred in.
 termCounts :: Corpus -> Text -> Int
diff --git a/tests/src/Data/DefaultMapTests.hs b/tests/src/Data/DefaultMapTests.hs
new file mode 100644
--- /dev/null
+++ b/tests/src/Data/DefaultMapTests.hs
@@ -0,0 +1,28 @@
+module Data.DefaultMapTests where
+
+import Test.QuickCheck (Arbitrary, arbitrary)
+import Test.QuickCheck.Instances ()
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+import Test.Framework ( testGroup, Test )
+
+import Data.Serialize (decode, encode)
+
+import Data.DefaultMap (DefaultMap(..), fromList)
+
+tests :: Test
+tests = testGroup "NLP.Data.DefaultMapTests"
+        [ testGroup "Serialize / Deserialize Tests"
+          [ testProperty "DefaultMap round-trips" prop_defMapSerialize
+          ]
+        ]
+
+instance (Arbitrary k, Arbitrary v, Ord k) => Arbitrary (DefaultMap k v) where
+  arbitrary = do
+      def <- arbitrary
+      entries <- arbitrary
+      return $ fromList def entries
+
+prop_defMapSerialize :: DefaultMap String String -> Bool
+prop_defMapSerialize c = case (decode . encode) c of
+                           Right c' -> c == c'
+                           Left _ -> False
diff --git a/tests/src/Main.hs b/tests/src/Main.hs
--- a/tests/src/Main.hs
+++ b/tests/src/Main.hs
@@ -23,6 +23,8 @@
 import qualified NLP.Similarity.VectorSimTests as Vec
 import qualified NLP.POSTests as POS
 import qualified NLP.POS.UnambiguousTaggerTests as UT
+import qualified NLP.TypesTests as TypeTests
+import qualified Data.DefaultMapTests as DefMap
 
 import Corpora
 
@@ -57,6 +59,8 @@
         , Vec.tests
         , POS.tests
         , UT.tests
+        , TypeTests.tests
+        , DefMap.tests
         ]
 
 
diff --git a/tests/src/NLP/TypesTests.hs b/tests/src/NLP/TypesTests.hs
new file mode 100644
--- /dev/null
+++ b/tests/src/NLP/TypesTests.hs
@@ -0,0 +1,27 @@
+module NLP.TypesTests where
+
+import Test.QuickCheck (Arbitrary, arbitrary)
+import Test.QuickCheck.Instances ()
+import Test.Framework.Providers.QuickCheck2 (testProperty)
+import Test.Framework ( testGroup, Test )
+
+import Data.Serialize (decode, encode)
+import NLP.Types (mkCorpus, Corpus(..))
+
+
+tests :: Test
+tests = testGroup "NLP.Types"
+        [ testGroup "Serialize / Deserialize Tests"
+          [ testProperty "Corpus round-trips" prop_corpusSerialize
+          ]
+        ]
+
+instance Arbitrary Corpus where
+  arbitrary = do
+      docs <- arbitrary
+      return $ mkCorpus docs
+
+prop_corpusSerialize :: Corpus -> Bool
+prop_corpusSerialize c = case (decode . encode) c of
+                           Right c' -> c == c'
+                           Left _ -> False