diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -4,7 +4,6 @@
   reduce memory footprint (#7, thanks Bodigrim)
 * introduce `Boundary` type (#10, thanks Bodigrim)
 * export `isSingleton` function for `Interval` and `IntegerInterval` (#13)
-* add `Generic` instances for `Interval` and `IntegerInterval`
 * remove deprecated `EndPoint` data type (#14, thanks Bodigrim)
 
 1.3.1
diff --git a/data-interval.cabal b/data-interval.cabal
--- a/data-interval.cabal
+++ b/data-interval.cabal
@@ -1,5 +1,5 @@
 Name:		data-interval
-Version:	2.0.0
+Version:	2.0.1
 License:	BSD3
 License-File:	COPYING
 Author:		Masahiro Sakai (masahiro.sakai@gmail.com)
diff --git a/src/Data/IntegerInterval/Internal.hs b/src/Data/IntegerInterval/Internal.hs
--- a/src/Data/IntegerInterval/Internal.hs
+++ b/src/Data/IntegerInterval/Internal.hs
@@ -1,5 +1,5 @@
 {-# OPTIONS_GHC -Wall #-}
-{-# LANGUAGE CPP, DeriveDataTypeable, DeriveGeneric, LambdaCase #-}
+{-# LANGUAGE CPP, DeriveDataTypeable, LambdaCase #-}
 {-# LANGUAGE Safe #-}
 #if __GLASGOW_HASKELL__ >= 708
 {-# LANGUAGE RoleAnnotations #-}
@@ -17,7 +17,6 @@
 import Data.Data
 import Data.ExtendedReal
 import Data.Hashable
-import GHC.Generics (Generic)
 
 infix 5 <=..<=
 
@@ -29,7 +28,7 @@
   | LessOrEqual !Integer
   | GreaterOrEqual !Integer
   | BothClosed !Integer !Integer
-  deriving (Eq, Generic, Typeable)
+  deriving (Eq, Typeable)
 
 -- | Lower endpoint (/i.e./ greatest lower bound)  of the interval.
 --
@@ -80,9 +79,23 @@
 intervalDataType :: DataType
 intervalDataType = mkDataType "Data.IntegerInterval.Internal.IntegerInterval" [intervalConstr]
 
-instance NFData IntegerInterval
+instance NFData IntegerInterval where
+  rnf = \case
+    Whole            -> ()
+    Empty            -> ()
+    Point r          -> rnf r
+    LessOrEqual r    -> rnf r
+    GreaterOrEqual r -> rnf r
+    BothClosed p q   -> rnf p `seq` rnf q
 
-instance Hashable IntegerInterval
+instance Hashable IntegerInterval where
+  hashWithSalt s = \case
+    Whole            -> s `hashWithSalt`  (1 :: Int)
+    Empty            -> s `hashWithSalt`  (2 :: Int)
+    Point r          -> s `hashWithSalt`  (3 :: Int) `hashWithSalt` r
+    LessOrEqual r    -> s `hashWithSalt`  (4 :: Int) `hashWithSalt` r
+    GreaterOrEqual r -> s `hashWithSalt`  (5 :: Int) `hashWithSalt` r
+    BothClosed p q   -> s `hashWithSalt`  (6 :: Int) `hashWithSalt` p `hashWithSalt` q
 
 -- | closed interval [@l@,@u@]
 (<=..<=)
diff --git a/src/Data/Interval/Internal.hs b/src/Data/Interval/Internal.hs
--- a/src/Data/Interval/Internal.hs
+++ b/src/Data/Interval/Internal.hs
@@ -46,7 +46,7 @@
   | LeftOpen !r !r
   | RightOpen !r !r
   | BothOpen !r !r
-  deriving (Eq, Generic, Typeable)
+  deriving (Eq, Typeable)
 
 -- | Lower endpoint (/i.e./ greatest lower bound) of the interval,
 -- together with 'Boundary' information.
@@ -101,9 +101,33 @@
 intervalDataType :: DataType
 intervalDataType = mkDataType "Data.Interval.Internal.Interval" [intervalConstr]
 
-instance NFData r => NFData (Interval r)
+instance NFData r => NFData (Interval r) where
+  rnf = \case
+    Whole            -> ()
+    Empty            -> ()
+    Point r          -> rnf r
+    LessThan r       -> rnf r
+    LessOrEqual r    -> rnf r
+    GreaterThan r    -> rnf r
+    GreaterOrEqual r -> rnf r
+    BothClosed p q   -> rnf p `seq` rnf q
+    LeftOpen p q     -> rnf p `seq` rnf q
+    RightOpen p q    -> rnf p `seq` rnf q
+    BothOpen p q     -> rnf p `seq` rnf q
 
-instance Hashable r => Hashable (Interval r)
+instance Hashable r => Hashable (Interval r) where
+  hashWithSalt s = \case
+    Whole            -> s `hashWithSalt`  (1 :: Int)
+    Empty            -> s `hashWithSalt`  (2 :: Int)
+    Point r          -> s `hashWithSalt`  (3 :: Int) `hashWithSalt` r
+    LessThan r       -> s `hashWithSalt`  (4 :: Int) `hashWithSalt` r
+    LessOrEqual r    -> s `hashWithSalt`  (5 :: Int) `hashWithSalt` r
+    GreaterThan r    -> s `hashWithSalt`  (6 :: Int) `hashWithSalt` r
+    GreaterOrEqual r -> s `hashWithSalt`  (7 :: Int) `hashWithSalt` r
+    BothClosed p q   -> s `hashWithSalt`  (8 :: Int) `hashWithSalt` p `hashWithSalt` q
+    LeftOpen p q     -> s `hashWithSalt`  (9 :: Int) `hashWithSalt` p `hashWithSalt` q
+    RightOpen p q    -> s `hashWithSalt` (10 :: Int) `hashWithSalt` p `hashWithSalt` q
+    BothOpen p q     -> s `hashWithSalt` (11 :: Int) `hashWithSalt` p `hashWithSalt` q
 
 -- | empty (contradicting) interval
 empty :: Ord r => Interval r