diff --git a/looksee.cabal b/looksee.cabal
--- a/looksee.cabal
+++ b/looksee.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           looksee
-version:        0.8.2
+version:        0.8.3
 synopsis:       A simple text parser with decent errors
 description:    Please see the README on GitHub at <https://github.com/ejconlon/looksee#readme>
 category:       Parsing
@@ -67,6 +67,7 @@
     , bifunctors >=5.5 && <5.7
     , containers >=0.6 && <0.8
     , errata >=0.4.0.1 && <0.5
+    , hashable >=1.4 && <1.6
     , mmorph ==1.2.*
     , mtl >=2.2 && <2.4
     , recursion-schemes ==5.2.*
@@ -115,6 +116,7 @@
     , bifunctors >=5.5 && <5.7
     , containers >=0.6 && <0.8
     , errata >=0.4.0.1 && <0.5
+    , hashable >=1.4 && <1.6
     , looksee
     , mmorph ==1.2.*
     , mtl >=2.2 && <2.4
diff --git a/src/Looksee.hs b/src/Looksee.hs
--- a/src/Looksee.hs
+++ b/src/Looksee.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE UndecidableInstances #-}
@@ -101,6 +102,8 @@
   )
 where
 
+import Data.Hashable (Hashable)
+import GHC.Generics (Generic)
 import Control.Applicative (Alternative (..))
 import Control.Exception (Exception)
 import Control.Monad (ap, void)
@@ -141,7 +144,8 @@
 
 -- | A generic span, used for tracking ranges of offsets or (line, col)
 data Span a = Span {spanStart :: !a, spanEnd :: !a}
-  deriving stock (Eq, Ord, Show, Functor, Foldable, Traversable)
+  deriving stock (Eq, Ord, Show, Functor, Foldable, Traversable, Generic)
+  deriving anyclass (Hashable)
 
 -- | Auxiliary data structure to translate offsets to (line, col)
 type LineColLookup = Vector (Int, Int)
@@ -310,9 +314,9 @@
 instance MFunctor (T e) where
   hoist mn (T x) = T (hoist (hoist mn) x)
 
-deriving instance (MonadReader r m) => MonadReader r (T e m)
+deriving newtype instance (MonadReader r m) => MonadReader r (T e m)
 
-deriving instance (MonadWriter w m) => MonadWriter w (T e m)
+deriving newtype instance (MonadWriter w m) => MonadWriter w (T e m)
 
 -- private
 runT :: T e m a -> St -> m (Either (Err e) a, St)