diff --git a/.hlint.yaml b/.hlint.yaml
--- a/.hlint.yaml
+++ b/.hlint.yaml
@@ -1,4 +1,4 @@
-- arguments: [--cpp-define=HLINT, --cpp-ansi, --cpp-include=include]
+- arguments: [-XCPP, --cpp-define=HLINT, --cpp-ansi, --cpp-include=include]
 
 - fixity: "infixr 8 **!, <**>"
 - fixity: "infixl 7 *!, /!, ^*, *^, ^/"
diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,3 +1,7 @@
+4.5.1 [2022.05.18]
+------------------
+* Allow building with `transformers-0.6.*`.
+
 4.5 [2021.11.07]
 ----------------
 * The build-type has been changed from `Custom` to `Simple`.
diff --git a/ad.cabal b/ad.cabal
--- a/ad.cabal
+++ b/ad.cabal
@@ -1,5 +1,5 @@
 name:          ad
-version:       4.5
+version:       4.5.1
 license:       BSD3
 license-File:  LICENSE
 copyright:     (c) Edward Kmett 2010-2021,
@@ -18,8 +18,8 @@
              , GHC == 8.6.5
              , GHC == 8.8.4
              , GHC == 8.10.7
-             , GHC == 9.0.1
-             , GHC == 9.2.1
+             , GHC == 9.0.2
+             , GHC == 9.2.2
 synopsis:      Automatic Differentiation
 extra-source-files:
   .gitignore
@@ -123,7 +123,7 @@
     nats             >= 0.1.2   && < 2,
     reflection       >= 1.4     && < 3,
     semigroups       >= 0.16    && < 1,
-    transformers     >= 0.5.2.0 && < 0.6
+    transformers     >= 0.5.2.0 && < 0.7
 
   if impl(ghc < 7.8)
     build-depends: tagged >= 0.7 && < 1
diff --git a/src/Numeric/AD/Internal/Or.hs b/src/Numeric/AD/Internal/Or.hs
--- a/src/Numeric/AD/Internal/Or.hs
+++ b/src/Numeric/AD/Internal/Or.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE DeriveDataTypeable #-}
diff --git a/src/Numeric/AD/Mode.hs b/src/Numeric/AD/Mode.hs
--- a/src/Numeric/AD/Mode.hs
+++ b/src/Numeric/AD/Mode.hs
@@ -9,6 +9,7 @@
 {-# LANGUAGE ViewPatterns #-}
 {-# LANGUAGE Rank2Types #-}
 {-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE UndecidableInstances #-}
 -----------------------------------------------------------------------------
 -- |