diff --git a/CHANGES b/CHANGES
--- a/CHANGES
+++ b/CHANGES
@@ -1,4 +1,9 @@
+= Version 1.3.0.0, 2012-12-11 =
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+* Add NFData instances.
+
 = Version 1.2.0.1, 2011-09-21 =
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 * Add missing StandaloneDeriving and DeriveDataTypeable
 GHC extensions to enable Typeable deriving. Also remove
 PatternGuards extension, which was needed only once.
diff --git a/Data/HashMap.hs b/Data/HashMap.hs
--- a/Data/HashMap.hs
+++ b/Data/HashMap.hs
@@ -117,6 +117,7 @@
 import Prelude hiding (lookup,map,filter,null)
 
 import Control.Applicative (Applicative(pure,(<*>)))
+import Control.DeepSeq
 import Data.Hashable
 import Data.Foldable (Foldable(foldMap))
 import Data.List (foldl')
@@ -156,6 +157,10 @@
 
 data Some k v = Only !k v | More !(M.Map k v) deriving (Eq, Ord)
 
+instance (NFData k, NFData v) => NFData (Some k v) where
+  rnf (Only k v) = rnf k `seq` rnf v
+  rnf (More m) = rnf m
+
 -- | The abstract type of a @Map@. Its interface is a suitable
 -- subset of 'Data.IntMap.IntMap'.
 newtype Map k v = Map (I.IntMap (Some k v)) deriving (Eq, Ord)
@@ -164,6 +169,9 @@
 -- It is deprecated and will be removed in furture releases.
 {-# DEPRECATED HashMap "HashMap is deprecated. Please use Map instead." #-}
 type HashMap k v = Map k v
+
+instance (NFData k, NFData v) => NFData (Map k v) where
+  rnf (Map m) = rnf m
 
 instance Functor (Map k) where
   fmap = map
diff --git a/Data/HashSet.hs b/Data/HashSet.hs
--- a/Data/HashSet.hs
+++ b/Data/HashSet.hs
@@ -69,6 +69,7 @@
 
 import Prelude hiding (lookup,map,filter,null)
 
+import Control.DeepSeq
 import Data.Hashable
 import Data.List (foldl')
 import Data.Monoid (Monoid(..))
@@ -98,6 +99,10 @@
 
 data Some a = Only !a | More !(S.Set a) deriving (Eq, Ord)
 
+instance NFData a => NFData (Some a) where
+  rnf (Only a) = rnf a
+  rnf (More s) = rnf s
+
 -- | The abstract type of a @Set@. Its interface is a suitable
 -- subset of 'Data.IntSet.IntSet'.
 newtype Set a = Set (I.IntMap (Some a)) deriving (Eq, Ord)
@@ -106,6 +111,9 @@
 -- It is deprecated and will be removed in furture releases.
 {-# DEPRECATED HashSet "HashSet is deprecated. Please use Set instead." #-}
 type HashSet a = Set a
+
+instance NFData a => NFData (Set a) where
+  rnf (Set s) = rnf s
 
 instance Ord a => Monoid (Set a) where
   mempty  = empty
diff --git a/hashmap.cabal b/hashmap.cabal
--- a/hashmap.cabal
+++ b/hashmap.cabal
@@ -1,5 +1,5 @@
 Name:                hashmap
-Version:             1.2.0.1
+Version:             1.3.0.0
 Synopsis:            Persistent containers Map and Set based on hashing.
 Description:         An implementation of persistent 'Map' and 'Set' containers
                      based on hashing. The implementation is build on
@@ -32,7 +32,8 @@
   Exposed-modules:   Data.HashMap, Data.HashSet
 
   Build-depends:     base >= 4.0 && < 5,
-                     containers >= 0.3,
+                     containers >= 0.4.2,
+                     deepseq >= 1.2,
                      hashable >= 1.0
 
   Extensions:        CPP