diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+## Megaparsec 9.0.1
+
+* Added [Safe
+  Haskell](https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/safe_haskell.html)
+  support.
+
 ## Megaparsec 9.0.0
 
 * Split the `Stream` type class. The methods `showTokens` and `tokensLength`
diff --git a/Text/Megaparsec.hs b/Text/Megaparsec.hs
--- a/Text/Megaparsec.hs
+++ b/Text/Megaparsec.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UndecidableInstances #-}
diff --git a/Text/Megaparsec/Byte.hs b/Text/Megaparsec/Byte.hs
--- a/Text/Megaparsec/Byte.hs
+++ b/Text/Megaparsec/Byte.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 
diff --git a/Text/Megaparsec/Byte/Lexer.hs b/Text/Megaparsec/Byte/Lexer.hs
--- a/Text/Megaparsec/Byte/Lexer.hs
+++ b/Text/Megaparsec/Byte/Lexer.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE Trustworthy #-}
 {-# LANGUAGE TypeFamilies #-}
 
 -- |
diff --git a/Text/Megaparsec/Char.hs b/Text/Megaparsec/Char.hs
--- a/Text/Megaparsec/Char.hs
+++ b/Text/Megaparsec/Char.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 
@@ -118,7 +119,7 @@
 
 -- | Like 'space1', but does not accept newlines and carriage returns.
 --
--- @since 8.0.0
+-- @since 9.0.0
 hspace1 :: (MonadParsec e s m, Token s ~ Char) => m ()
 hspace1 = void $ takeWhile1P (Just "white space") isHSpace
 {-# INLINE hspace1 #-}
diff --git a/Text/Megaparsec/Char/Lexer.hs b/Text/Megaparsec/Char/Lexer.hs
--- a/Text/Megaparsec/Char/Lexer.hs
+++ b/Text/Megaparsec/Char/Lexer.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE Trustworthy #-}
 {-# LANGUAGE TypeFamilies #-}
 
 -- |
diff --git a/Text/Megaparsec/Class.hs b/Text/Megaparsec/Class.hs
--- a/Text/Megaparsec/Class.hs
+++ b/Text/Megaparsec/Class.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE UndecidableInstances #-}
 
diff --git a/Text/Megaparsec/Common.hs b/Text/Megaparsec/Common.hs
--- a/Text/Megaparsec/Common.hs
+++ b/Text/Megaparsec/Common.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE Safe #-}
 
 -- |
 -- Module      :  Text.Megaparsec.Common
diff --git a/Text/Megaparsec/Debug.hs b/Text/Megaparsec/Debug.hs
--- a/Text/Megaparsec/Debug.hs
+++ b/Text/Megaparsec/Debug.hs
@@ -1,5 +1,6 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE Unsafe #-}
 
 -- |
 -- Module      :  Text.Megaparsec.Debug
diff --git a/Text/Megaparsec/Error.hs b/Text/Megaparsec/Error.hs
--- a/Text/Megaparsec/Error.hs
+++ b/Text/Megaparsec/Error.hs
@@ -6,6 +6,7 @@
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE UndecidableInstances #-}
diff --git a/Text/Megaparsec/Error/Builder.hs b/Text/Megaparsec/Error/Builder.hs
--- a/Text/Megaparsec/Error/Builder.hs
+++ b/Text/Megaparsec/Error/Builder.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE UndecidableInstances #-}
diff --git a/Text/Megaparsec/Internal.hs b/Text/Megaparsec/Internal.hs
--- a/Text/Megaparsec/Internal.hs
+++ b/Text/Megaparsec/Internal.hs
@@ -1,10 +1,10 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UndecidableInstances #-}
@@ -86,8 +86,13 @@
 -- unexpected 'a'
 -- expecting 'r' or end of input
 newtype Hints t = Hints [Set (ErrorItem t)]
-  deriving (Semigroup, Monoid)
 
+instance Semigroup (Hints t) where
+  Hints xs <> Hints ys = Hints $ xs <> ys
+
+instance Monoid (Hints t) where
+  mempty = Hints mempty
+
 -- | All information available after parsing. This includes consumption of
 -- input, success (with returned value) or failure (with parse error), and
 -- parser state at the end of parsing.
@@ -280,6 +285,15 @@
         Error e -> eerr e s'
 
 -- | 'mzero' is a parser that __fails__ without consuming input.
+--
+-- __Note__: strictly speaking, this instance is unlawful. The right
+-- identity law is does not hold, e.g. in general this is not true:
+--
+-- > v >> mzero = mero
+--
+-- However the following holds:
+--
+-- > try v >> mzero = mzero
 instance (Ord e, Stream s) => MonadPlus (ParsecT e s m) where
   mzero = pZero
   mplus = pPlus
diff --git a/Text/Megaparsec/Lexer.hs b/Text/Megaparsec/Lexer.hs
--- a/Text/Megaparsec/Lexer.hs
+++ b/Text/Megaparsec/Lexer.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE Safe #-}
 
 -- |
 -- Module      :  Text.Megaparsec.Common
diff --git a/Text/Megaparsec/Pos.hs b/Text/Megaparsec/Pos.hs
--- a/Text/Megaparsec/Pos.hs
+++ b/Text/Megaparsec/Pos.hs
@@ -1,6 +1,7 @@
+{-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DeriveGeneric #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE Safe #-}
 
 -- |
 -- Module      :  Text.Megaparsec.Pos
@@ -48,7 +49,7 @@
 --
 -- @since 5.0.0
 newtype Pos = Pos Int
-  deriving (Show, Eq, Ord, Data, Typeable, NFData)
+  deriving (Show, Eq, Ord, Data, Generic, Typeable, NFData)
 
 -- | Construction of 'Pos' from 'Int'. The function throws
 -- 'InvalidPosException' when given a non-positive argument.
diff --git a/Text/Megaparsec/State.hs b/Text/Megaparsec/State.hs
--- a/Text/Megaparsec/State.hs
+++ b/Text/Megaparsec/State.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE UndecidableInstances #-}
 
diff --git a/Text/Megaparsec/Stream.hs b/Text/Megaparsec/Stream.hs
--- a/Text/Megaparsec/Stream.hs
+++ b/Text/Megaparsec/Stream.hs
@@ -4,6 +4,7 @@
 {-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE Safe #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 
diff --git a/megaparsec.cabal b/megaparsec.cabal
--- a/megaparsec.cabal
+++ b/megaparsec.cabal
@@ -1,6 +1,6 @@
 cabal-version:   1.18
 name:            megaparsec
-version:         9.0.0
+version:         9.0.1
 license:         BSD2
 license-file:    LICENSE.md
 maintainer:      Mark Karpov <markkarpov92@gmail.com>
@@ -9,7 +9,7 @@
     Paolo Martini <paolo@nemail.it>,
     Daan Leijen <daan@microsoft.com>
 
-tested-with:     ghc ==8.6.5 ghc ==8.8.4 ghc ==8.10.1
+tested-with:     ghc ==8.6.5 ghc ==8.8.4 ghc ==8.10.2
 homepage:        https://github.com/mrkkrp/megaparsec
 bug-reports:     https://github.com/mrkkrp/megaparsec/issues
 synopsis:        Monadic parser combinators