diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+## 0.4.1 *January 1st 2021*
+* Support for GHC-9.0.1-rc1
+
 ## 0.4 *January 31st 2020*
 * Expose functions for flattening constraints in GHC 8.2 and earlier
 
diff --git a/ghc-tcplugins-extra.cabal b/ghc-tcplugins-extra.cabal
--- a/ghc-tcplugins-extra.cabal
+++ b/ghc-tcplugins-extra.cabal
@@ -1,5 +1,5 @@
 name:                ghc-tcplugins-extra
-version:             0.4
+version:             0.4.1
 synopsis:            Utilities for writing GHC type-checker plugins
 description:         Utilities for writing GHC type-checker plugins, such as
                      creating constraints, with a stable API covering multiple
@@ -18,7 +18,7 @@
                      CHANGELOG.md
 cabal-version:       >=1.10
 tested-with:         GHC == 7.10.3, GHC == 8.0.2, GHC == 8.2.2, GHC == 8.4.4,
-                     GHC == 8.6.5, GHC == 8.8.2, GHC == 8.10.1
+                     GHC == 8.6.5, GHC == 8.8.4, GHC == 8.10.3, GHC == 9.0.1
 
 source-repository head
   type: git
@@ -33,7 +33,7 @@
 library
   exposed-modules:     GHC.TcPluginM.Extra
   build-depends:       base >=4.8  && <5,
-                       ghc  >=7.10 && <8.12
+                       ghc  >=7.10 && <9.2
   hs-source-dirs:      src
   default-language:    Haskell2010
   other-extensions:    CPP
diff --git a/src/GHC/TcPluginM/Extra.hs b/src/GHC/TcPluginM/Extra.hs
--- a/src/GHC/TcPluginM/Extra.hs
+++ b/src/GHC/TcPluginM/Extra.hs
@@ -39,11 +39,32 @@
 where
 
 -- External
-#if __GLASGOW_HASKELL__ < 711
 import Data.Maybe (mapMaybe)
-#endif
+import Control.Arrow (first, second)
+import Data.Function (on)
+import Data.List     (groupBy, partition, sortOn)
 
 -- GHC API
+#if MIN_VERSION_ghc(9,0,0)
+import GHC.Core (Expr (..))
+import GHC.Core.Coercion (Role (..), mkPrimEqPred, mkUnivCo)
+import GHC.Core.Type  (PredType)
+import GHC.Core.TyCo.Rep (Type (..), UnivCoProvenance (..))
+import GHC.Data.FastString (FastString, fsLit)
+import qualified GHC.Driver.Finder as Finder
+import GHC.Unit.Module (Module, ModuleName)
+import GHC.Tc.Plugin (FindResult (..), TcPluginM, lookupOrig, tcPluginTrace)
+import qualified GHC.Tc.Plugin as TcPluginM
+import GHC.Tc.Utils.TcType (TcTyVar, TcType)
+import GHC.Tc.Types (TcPlugin (..), TcPluginResult (..))
+import GHC.Tc.Types.Constraint
+  (Ct (..), CtLoc, CtEvidence (..), ctEvId, ctLoc, mkNonCanonical)
+import GHC.Tc.Types.Evidence (EvTerm (..))
+import GHC.Types.Name (Name)
+import GHC.Types.Name.Occurrence (OccName)
+import GHC.Utils.Outputable ((<+>), ($$), empty, ppr, text)
+import GHC.Utils.Panic (panicDoc)
+#else
 #if __GLASGOW_HASKELL__ < 711
 import BasicTypes (TopLevelFlag (..))
 #endif
@@ -90,9 +111,6 @@
 import Type       (EqRel (..), PredTree (..), PredType, Type, classifyPredType)
 import Var        (varType)
 #endif
-import Control.Arrow (first, second)
-import Data.Function (on)
-import Data.List     (groupBy, partition, sortOn)
 #if __GLASGOW_HASKELL__ < 809
 import TcRnTypes     (Ct (..), ctLoc, ctEvId, mkNonCanonical)
 #else
@@ -109,9 +127,9 @@
 import TcRnTypes     (ctEvTerm)
 import TypeRep       (Type (..))
 #else
-import Data.Maybe    (mapMaybe)
 import TyCoRep       (Type (..))
 #endif
+#endif
 
 -- workaround for https://ghc.haskell.org/trac/ghc/ticket/10301
 #if __GLASGOW_HASKELL__ < 802
@@ -389,7 +407,10 @@
   -- TODO: Is it safe to do "dumb" substitution under binders?
   -- ForAllTy tv (substType subst ty)
   t
-#if __GLASGOW_HASKELL__ >= 809
+#if __GLASGOW_HASKELL__ >= 900
+substType subst (FunTy k1 k2 t1 t2) =
+  FunTy k1 k2 (substType subst t1) (substType subst t2)
+#elif __GLASGOW_HASKELL__ >= 809
 substType subst (FunTy af t1 t2) =
   FunTy af (substType subst t1) (substType subst t2)
 #elif __GLASGOW_HASKELL__ >= 802