diff --git a/hie-compat/hie-compat.cabal b/hie-compat/hie-compat.cabal
index 9778485028..7ceccc51ab 100644
--- a/hie-compat/hie-compat.cabal
+++ b/hie-compat/hie-compat.cabal
@@ -23,11 +23,13 @@ flag ghc-lib
 library
   default-language:    Haskell2010
   build-depends:
-     base < 4.15, array, bytestring, containers, directory, filepath, transformers
+     base < 4.16, array, bytestring, containers, directory, filepath, transformers
   if flag(ghc-lib)
     build-depends: ghc-lib
   else
     build-depends: ghc, ghc-boot
+  if (impl(ghc >= 9.0) && impl(ghc < 9.1))
+    ghc-options: -Wall -Wno-name-shadowing
 
   exposed-modules:
     Compat.HieAst
@@ -38,8 +40,10 @@ library
 
   if (impl(ghc > 8.5) && impl(ghc < 8.7) && !flag(ghc-lib))
     hs-source-dirs: src-ghc86
-  if (impl(ghc > 8.7) && impl(ghc < 8.10)) 
+  if (impl(ghc > 8.7) && impl(ghc < 8.10))
     hs-source-dirs: src-ghc88 src-reexport
-  if (impl(ghc > 8.9) && impl(ghc < 8.11) || flag(ghc-lib))
+  if (impl(ghc > 8.9) && impl(ghc < 8.11))
     hs-source-dirs: src-ghc810 src-reexport
+  if (impl(ghc >= 9.0) && impl(ghc < 9.1) || flag(ghc-lib))
+    hs-source-dirs: src-ghc901
 
diff --git a/hie-compat/src-ghc901/Compat/HieAst.hs b/hie-compat/src-ghc901/Compat/HieAst.hs
new file mode 100644
index 0000000000..26f315caef
--- /dev/null
+++ b/hie-compat/src-ghc901/Compat/HieAst.hs
@@ -0,0 +1,35 @@
+{-
+Forked from GHC v9.0.1 to work around the readFile side effect in mkHiefile
+
+Main functions for .hie file generation
+-}
+{- HLINT ignore -}
+{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
+
+module Compat.HieAst ( mkHieFile, enrichHie ) where
+
+import           GHC.Data.Maybe      (expectJust)
+import           GHC.Driver.Types
+import           GHC.Hs
+import           GHC.Tc.Types        (TcGblEnv)
+import           GHC.Types.Avail     (Avails)
+import           GHC.Unit.Module     (ml_hs_file)
+
+import           GHC.Iface.Ext.Ast   (enrichHie, mkHieFileWithSource)
+import           GHC.Iface.Ext.Types
+
+import qualified Data.ByteString     as BS
+
+
+type RenamedSource     = ( HsGroup GhcRn, [LImportDecl GhcRn]
+                         , Maybe [(LIE GhcRn, Avails)]
+                         , Maybe LHsDocString )
+
+-- | Construct an 'HieFile' from the outputs of the typechecker.
+mkHieFile :: ModSummary
+          -> TcGblEnv
+          -> RenamedSource
+          -> BS.ByteString -> Hsc HieFile
+mkHieFile ms ts rs src = do
+  let src_file = expectJust "mkHieFile" (ml_hs_file $ ms_location ms)
+  mkHieFileWithSource src_file src ms ts rs
diff --git a/hie-compat/src-ghc901/Compat/HieBin.hs b/hie-compat/src-ghc901/Compat/HieBin.hs
new file mode 100644
index 0000000000..254e1db6d3
--- /dev/null
+++ b/hie-compat/src-ghc901/Compat/HieBin.hs
@@ -0,0 +1,8 @@
+{-
+Binary serialization for .hie files.
+-}
+
+module Compat.HieBin ( module GHC.Iface.Ext.Binary)
+where
+
+import GHC.Iface.Ext.Binary
diff --git a/hie-compat/src-ghc901/Compat/HieDebug.hs b/hie-compat/src-ghc901/Compat/HieDebug.hs
new file mode 100644
index 0000000000..872da67c2b
--- /dev/null
+++ b/hie-compat/src-ghc901/Compat/HieDebug.hs
@@ -0,0 +1,10 @@
+module Compat.HieDebug
+  ( module GHC.Iface.Ext.Debug
+  , ppHie ) where
+import GHC.Iface.Ext.Debug
+
+import GHC.Iface.Ext.Types (HieAST)
+import GHC.Utils.Outputable (Outputable(ppr), SDoc)
+
+ppHie :: Outputable a => HieAST a -> SDoc
+ppHie = ppr
diff --git a/hie-compat/src-ghc901/Compat/HieTypes.hs b/hie-compat/src-ghc901/Compat/HieTypes.hs
new file mode 100644
index 0000000000..36bb86abeb
--- /dev/null
+++ b/hie-compat/src-ghc901/Compat/HieTypes.hs
@@ -0,0 +1,3 @@
+module Compat.HieTypes
+  ( module GHC.Iface.Ext.Types ) where
+import GHC.Iface.Ext.Types
diff --git a/hie-compat/src-ghc901/Compat/HieUtils.hs b/hie-compat/src-ghc901/Compat/HieUtils.hs
new file mode 100644
index 0000000000..204a312039
--- /dev/null
+++ b/hie-compat/src-ghc901/Compat/HieUtils.hs
@@ -0,0 +1,3 @@
+module Compat.HieUtils
+  ( module GHC.Iface.Ext.Utils ) where
+import GHC.Iface.Ext.Utils