diff --git a/src/Nix/Builtins.hs b/src/Nix/Builtins.hs
index 9e0e90aef..caf1314d4 100644
--- a/src/Nix/Builtins.hs
+++ b/src/Nix/Builtins.hs
@@ -19,7 +19,6 @@
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE ViewPatterns #-}
 
-{-# OPTIONS_GHC -Wno-missing-signatures #-}
 {-# OPTIONS_GHC -fno-warn-name-shadowing #-}
 
 -- | Code that implements Nix builtins. Lists the functions that are built into the Nix expression evaluator. Some built-ins (aka `derivation`), are always in the scope, so they can be accessed by the name. To keap the namespace clean, most built-ins are inside the `builtins` scope - a set that contains all what is a built-in.
@@ -660,6 +659,7 @@ splitMatches numDropped (((_, (start, len)) : captures) : mts) haystack =
   caps           = nvList (map f captures)
   f (a, (s, _)) = if s < 0 then nvConstant NNull else thunkStr a
 
+thunkStr :: Applicative f => ByteString -> NValue t f m
 thunkStr s = nvStr (makeNixStringWithoutContext (decodeUtf8 s))
 
 substring :: forall e t f m. MonadNix e t f m => Int -> Int -> NixString -> Prim m NixString
@@ -1513,16 +1513,16 @@ newtype Prim m a = Prim { runPrim :: m a }
 
 -- | Types that support conversion to nix in a particular monad
 class ToBuiltin t f m a | a -> m where
-    toBuiltin :: String -> a -> m (NValue t f m)
+  toBuiltin :: String -> a -> m (NValue t f m)
 
 instance (MonadNix e t f m, ToValue a m (NValue t f m))
-      => ToBuiltin t f m (Prim m a) where
+         => ToBuiltin t f m (Prim m a) where
   toBuiltin _ p = toValue =<< runPrim p
 
 instance ( MonadNix e t f m
          , FromValue a m (Deeper (NValue t f m))
          , ToBuiltin t f m b
          )
-      => ToBuiltin t f m (a -> b) where
+         => ToBuiltin t f m (a -> b) where
   toBuiltin name f =
     pure $ nvBuiltin name (fromValue . Deeper >=> toBuiltin name . f)
diff --git a/src/Nix/Convert.hs b/src/Nix/Convert.hs
index ec228c783..7fe84cfac 100644
--- a/src/Nix/Convert.hs
+++ b/src/Nix/Convert.hs
@@ -13,7 +13,6 @@
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UndecidableInstances #-}
 
-{-# OPTIONS_GHC -Wno-missing-signatures #-}
 {-# OPTIONS_GHC -fno-warn-name-shadowing #-}
 
 -- | Although there are a lot of instances in this file, really it's just a
diff --git a/src/Nix/Exec.hs b/src/Nix/Exec.hs
index c5bf60b74..855243059 100644
--- a/src/Nix/Exec.hs
+++ b/src/Nix/Exec.hs
@@ -15,7 +15,6 @@
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UndecidableInstances #-}
 
-{-# OPTIONS_GHC -Wno-missing-signatures #-}
 {-# OPTIONS_GHC -Wno-orphans #-}
 {-# OPTIONS_GHC -fno-warn-name-shadowing #-}
 
diff --git a/src/Nix/Lint.hs b/src/Nix/Lint.hs
index 1b0e2317b..2efc53452 100644
--- a/src/Nix/Lint.hs
+++ b/src/Nix/Lint.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE AllowAmbiguousTypes #-}
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE DeriveTraversable #-}
diff --git a/src/Nix/Thunk.hs b/src/Nix/Thunk.hs
index 30445d0d9..dfc51c4b1 100644
--- a/src/Nix/Thunk.hs
+++ b/src/Nix/Thunk.hs
@@ -2,7 +2,6 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE UndecidableInstances #-}
 
 module Nix.Thunk where
 
diff --git a/src/Nix/Value/Equal.hs b/src/Nix/Value/Equal.hs
index 1a8c16c4c..509c0317a 100644
--- a/src/Nix/Value/Equal.hs
+++ b/src/Nix/Value/Equal.hs
@@ -7,7 +7,6 @@
 {-# LANGUAGE DeriveTraversable #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE FunctionalDependencies #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE OverloadedStrings #-}
@@ -19,11 +18,9 @@
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeOperators #-}
-{-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE ViewPatterns #-}
 
 {-# OPTIONS_GHC -Wno-orphans #-}
-{-# OPTIONS_GHC -Wno-missing-signatures #-}
 {-# OPTIONS_GHC -Wno-missing-pattern-synonym-signatures #-}
 
 module Nix.Value.Equal where
@@ -90,7 +87,7 @@ isDerivationM f m = case M.lookup "type" m of
       Nothing -> pure False
 
 isDerivation :: Monad m => (t -> Maybe NixString) -> AttrSet t -> Bool
-isDerivation f = runIdentity . isDerivationM (\x -> Identity (f x))
+isDerivation f = runIdentity . isDerivationM (Identity . f)
 
 valueFEqM
   :: Monad n
diff --git a/tests/EvalTests.hs b/tests/EvalTests.hs
index fb4afdb86..58a3f58bb 100644
--- a/tests/EvalTests.hs
+++ b/tests/EvalTests.hs
@@ -3,9 +3,8 @@
 {-# LANGUAGE QuasiQuotes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TemplateHaskell #-}
-{-# LANGUAGE UndecidableInstances #-}
 
-{-# OPTIONS_GHC -Wno-missing-signatures -Wno-orphans #-}
+{-# OPTIONS_GHC -Wno-missing-signatures #-}
 
 module EvalTests (tests, genEvalCompareTests) where
 
diff --git a/tests/PrettyParseTests.hs b/tests/PrettyParseTests.hs
index 0589edf3b..984bcd294 100644
--- a/tests/PrettyParseTests.hs
+++ b/tests/PrettyParseTests.hs
@@ -5,9 +5,7 @@
 {-# LANGUAGE MonoLocalBinds #-}
 {-# LANGUAGE NoMonomorphismRestriction #-}
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE UndecidableInstances #-}
 
-{-# OPTIONS -Wno-orphans#-}
 
 module PrettyParseTests where