diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## Fourmolu 0.19.0.1
+
+* Fixed a performance regression introduced in 0.8.0.0. [Issue
+  1176](https://github.com/tweag/ormolu/issues/1176).
+
 ## Fourmolu 0.19.0.0
 
 * Add `haddock-location-signature`, to configure haddock location independently of `function-arrows` ([#376](https://github.com/fourmolu/fourmolu/issues/376))
@@ -17,7 +22,7 @@
   1166](https://github.com/tweag/ormolu/issues/1166).
 
 * Make multiline function signatures in RequiredTypeArguments consistent with
-  types [PR 1170](https://github.com/tweag/ormolu/pull/1170)
+  types [PR 1170](https://github.com/tweag/ormolu/pull/1170).
 
 * Correctly format single-line `MultiWayIf`s. [Issue
   1171](https://github.com/tweag/ormolu/issues/1171).
diff --git a/fourmolu.cabal b/fourmolu.cabal
--- a/fourmolu.cabal
+++ b/fourmolu.cabal
@@ -1,6 +1,6 @@
 cabal-version: 2.4
 name: fourmolu
-version: 0.19.0.0
+version: 0.19.0.1
 license: BSD-3-Clause
 license-file: LICENSE.md
 maintainer:
diff --git a/src/Ormolu/Utils/IO.hs b/src/Ormolu/Utils/IO.hs
--- a/src/Ormolu/Utils/IO.hs
+++ b/src/Ormolu/Utils/IO.hs
@@ -10,7 +10,6 @@
 where
 
 import Control.Exception (catch, throwIO)
-import Control.Monad (void)
 import Control.Monad.IO.Class
 import Data.IORef
 import Data.Map.Lazy (Map)
@@ -67,5 +66,5 @@
     Just v -> pure v
     Nothing -> do
       v <- action
-      void $ atomicModifyIORef cacheVar (pure . M.insert k v)
+      atomicModifyIORef cacheVar ((,()) . M.insert k v)
       pure v