diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,10 @@
 # Changelog for ghc-lib-parser-ex
 
+## 0.20201001 released 2020-09-01
+- Update to `ghc-lib-0.20201001`
+- `GHCLIB_API_811` -> `GHCLIB_API_HEAD`
+- Add support for `GHCLIB_API_900`
+
 ## 0.20200901 released 2020-09-01
 - Update to `ghc-lib-0.20200901`
 
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -27,7 +27,7 @@
 ```
 Run `stack runhaskell --package extra --package optparse-applicative CI.hs -- --help` for more options.
 
-To run [`hlint`](https://github.com/ndmitchell/hlint) on this repository, `hlint --cpp-include cbits --cpp-define GHCLIB_API_XXX .` (where `XXX` at this time is one of `808`, `810` or `811`).
+To run [`hlint`](https://github.com/ndmitchell/hlint) on this repository, `hlint --cpp-include cbits --cpp-define GHCLIB_API_XXX .` (where `XXX` at this time is one of `808`, `810` or `900`).
 
 ## Releasing `ghc-lib-parser-ex` (notes for maintainers)
 
diff --git a/cbits/ghclib_api.h b/cbits/ghclib_api.h
--- a/cbits/ghclib_api.h
+++ b/cbits/ghclib_api.h
@@ -6,23 +6,27 @@
 #if !defined(GHCLIB_API_H)
 #  define GHCLIB_API_H
 
-#  if !defined(GHCLIB_API_811) && !defined(GHCLIB_API_810) && !defined(GHCLIB_API_808)
+#  if !defined (GHCLIB_API_HEAD) && !defined (GHCLIB_API_900) && !defined (GHCLIB_API_810) && !defined (GHCLIB_API_808)
 #    if defined(MIN_VERSION_ghc_lib_parser)
-#       if !MIN_VERSION_ghc_lib_parser(1,  0,  0)
-#         define GHCLIB_API_811
-#       elif MIN_VERSION_ghc_lib_parser(8, 10, 0)
+#       if !MIN_VERSION_ghc_lib_parser( 1,  0,  0)
+#         define GHCLIB_API_HEAD
+#       elif MIN_VERSION_ghc_lib_parser(9,  0,  0)
+#         define GHCLIB_API_900
+#       elif MIN_VERSION_ghc_lib_parser(8, 10,  0)
 #         define GHCLIB_API_810
-#       elif MIN_VERSION_ghc_lib_parser(8,  8, 0)
+#       elif MIN_VERSION_ghc_lib_parser(8,  8,  0)
 #         define GHCLIB_API_808
 #       else
 #         error Unsupported GHC API version
 #      endif
 #    else
 #      if __GLASGOW_HASKELL__   == 811
-#        define GHCLIB_API_811
+#        define GHCLIB_API_HEAD
+#      elif __GLASGOW_HASKELL__ == 900
+#        define GHCLIB_API_900
 #      elif __GLASGOW_HASKELL__ == 810
 #        define GHCLIB_API_810
-#      elif __GLASGOW_HASKELL__  == 808
+#      elif __GLASGOW_HASKELL__ == 808
 #        define GHCLIB_API_808
 #      else
 #        error Unsupported GHC API version
diff --git a/ghc-lib-parser-ex.cabal b/ghc-lib-parser-ex.cabal
--- a/ghc-lib-parser-ex.cabal
+++ b/ghc-lib-parser-ex.cabal
@@ -1,6 +1,6 @@
 cabal-version: >= 1.18
 name:           ghc-lib-parser-ex
-version:        0.20200901
+version:        0.20201001
 description:    Please see the README on GitHub at <https://github.com/shayne-fletcher/ghc-lib-parser-ex#readme>
 homepage:       https://github.com/shayne-fletcher/ghc-lib-parser-ex#readme
 bug-reports:    https://github.com/shayne-fletcher/ghc-lib-parser-ex/issues
diff --git a/src/Language/Haskell/GhclibParserEx/Dump.hs b/src/Language/Haskell/GhclibParserEx/Dump.hs
--- a/src/Language/Haskell/GhclibParserEx/Dump.hs
+++ b/src/Language/Haskell/GhclibParserEx/Dump.hs
@@ -17,7 +17,7 @@
 
 #if !defined(MIN_VERSION_ghc_lib_parser)
 -- Using native ghc.
-#  if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#  if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_810)
 import GHC.Hs.Dump
 #  else
 import HsDumpAst
@@ -25,7 +25,7 @@
 #else
 -- Using ghc-lib-parser. Recent versions will include
 -- GHC.Hs.Dump (it got moved in from ghc-lib on 2020-02-05).
-# if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+# if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs.Dump
 #  else
 -- For simplicity, just assume it's missing from 8.8 ghc-lib-parser
@@ -40,7 +40,7 @@
 import Name
 import DataCon
 import SrcLoc
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs
 #else
 import HsSyn
diff --git a/src/Language/Haskell/GhclibParserEx/Fixity.hs b/src/Language/Haskell/GhclibParserEx/Fixity.hs
--- a/src/Language/Haskell/GhclibParserEx/Fixity.hs
+++ b/src/Language/Haskell/GhclibParserEx/Fixity.hs
@@ -16,7 +16,7 @@
   , infixr_, infixl_, infix_, fixity
   ) where
 
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Hs
 import GHC.Types.Basic
 import GHC.Types.Name.Reader
@@ -39,7 +39,7 @@
 import Data.Data hiding (Fixity)
 import Data.Generics.Uniplate.Data
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 noExt :: NoExtField
 noExt = noExtField
 #endif
@@ -59,7 +59,7 @@
 -- LPat and Pat have gone through a lot of churn. See
 -- https://gitlab.haskell.org/ghc/ghc/merge_requests/1925 for details.
 patFix :: [(String, Fixity)] -> LPat GhcPs -> LPat GhcPs
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 patFix fixities (L loc (ConPat _ op (InfixCon pat1 pat2))) =
   L loc (mkConOpPat (getFixities fixities) op (findFixity' (getFixities fixities) op) pat1 pat2)
 #elif defined (GHCLIB_API_810)
@@ -76,26 +76,26 @@
   -> Located RdrName -> Fixity
   -> LPat GhcPs -> LPat GhcPs
   -> Pat GhcPs
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 mkConOpPat fs op2 fix2 p1@(L loc (ConPat _ op1 (InfixCon p11 p12))) p2
 #elif defined (GHCLIB_API_810)
 mkConOpPat fs op2 fix2 p1@(L loc (ConPatIn op1 (InfixCon p11 p12))) p2
 #else
 mkConOpPat fs op2 fix2 p1@(dL->L loc (ConPatIn op1 (InfixCon p11 p12))) p2
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
   | nofix_error = ConPat noExtField op2 (InfixCon p1 p2)
 #else
   | nofix_error = ConPatIn op2 (InfixCon p1 p2)
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
   | associate_right = ConPat noExtField op1 (InfixCon p11 (L loc (mkConOpPat fs op2 fix2 p12 p2)))
 #elif defined (GHCLIB_API_810)
   | associate_right = ConPatIn op1 (InfixCon p11 (L loc (mkConOpPat fs op2 fix2 p12 p2)))
 #else
   | associate_right = ConPatIn op1 (InfixCon p11 (cL loc (mkConOpPat fs op2 fix2 p12 p2)))
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
   | otherwise = ConPat noExtField op2 (InfixCon p1 p2)
 #else
   | otherwise = ConPatIn op2 (InfixCon p1 p2)
@@ -103,7 +103,7 @@
   where
     fix1 = findFixity' fs op1
     (nofix_error, associate_right) = compareFixity fix1 fix2
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 mkConOpPat _ op _ p1 p2 = ConPat noExtField op (InfixCon p1 p2)
 #else
 mkConOpPat _ op _ p1 p2 = ConPatIn op (InfixCon p1 p2)
@@ -208,12 +208,12 @@
 fixity :: FixityDirection -> Int -> [String] -> [(String, Fixity)]
 fixity a p = map (,Fixity (SourceText "") p a)
 
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 fixitiesFromModule :: Located HsModule -> [(String, Fixity)]
 #else
 fixitiesFromModule :: Located (HsModule GhcPs) -> [(String, Fixity)]
 #endif
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 fixitiesFromModule (L _ (HsModule _ _ _ _ decls _ _)) = concatMap f decls
 #else
 fixitiesFromModule (L _ (HsModule _ _ _ decls _ _)) = concatMap f decls
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Driver/Flags.hs b/src/Language/Haskell/GhclibParserEx/GHC/Driver/Flags.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Driver/Flags.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Driver/Flags.hs
@@ -3,7 +3,7 @@
 #include "ghclib_api.h"
 module Language.Haskell.GhclibParserEx.GHC.Driver.Flags () where
 
-#if !defined(GHCLIB_API_811)
+#if !defined (GHCLIB_API_HEAD) && !defined (GHCLIB_API_900)
 import DynFlags
 #endif
 
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Driver/Session.hs b/src/Language/Haskell/GhclibParserEx/GHC/Driver/Session.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Driver/Session.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Driver/Session.hs
@@ -14,10 +14,10 @@
     , parsePragmasIntoDynFlags
   ) where
 
-#if defined(GHCLIB_API_808) || defined(GHCLIB_API_810)
+#if defined (GHCLIB_API_808) || defined (GHCLIB_API_810)
 import qualified GHC.LanguageExtensions as LangExt
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Utils.Panic
 import GHC.Parser.Header
 import GHC.Data.StringBuffer
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Hs.hs b/src/Language/Haskell/GhclibParserEx/GHC/Hs.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Hs.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Hs.hs
@@ -9,11 +9,11 @@
  )
 where
 
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Hs
 import GHC.Unit.Module
 import GHC.Types.SrcLoc
-#elif defined(GHCLIB_API_810)
+#elif defined (GHCLIB_API_810)
 import GHC.Hs
 import Module
 import SrcLoc
@@ -23,7 +23,7 @@
 import SrcLoc
 #endif
 
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 modName :: Located HsModule -> String
 #else
 modName :: Located (HsModule GhcPs) -> String
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Binds.hs b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Binds.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Binds.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Binds.hs
@@ -7,7 +7,7 @@
   )
 where
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs.Binds
 import GHC.Hs.Extension
 #else
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Decls.hs b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Decls.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Decls.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Decls.hs
@@ -7,12 +7,12 @@
     isNewType, isForD, isDerivD, isClsDefSig
   ) where
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs
 #else
 import HsSyn
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Types.SrcLoc
 #else
 import SrcLoc
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Expr.hs b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Expr.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Expr.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Expr.hs
@@ -16,12 +16,12 @@
   fromChar
   ) where
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs
 #else
 import HsSyn
 #endif
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Types.SrcLoc
 import GHC.Types.Name.Reader
 import GHC.Types.Name
@@ -99,7 +99,7 @@
 isParComp = \case ParStmt{} -> True; _ -> False
 
 isMDo :: HsStmtContext Name -> Bool
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 isMDo = \case MDoExpr _ -> True; _ -> False
 #else
 isMDo = \case MDoExpr -> True; _ -> False
@@ -138,7 +138,7 @@
 -- Field has a '_' as in '{foo=_} or is punned e.g. '{foo}'.
 isFieldWildcard :: LHsRecField GhcPs (LHsExpr GhcPs) -> Bool
 isFieldWildcard = \case
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
   (L _ HsRecField {hsRecFieldArg=(L _ (HsUnboundVar _ s))}) -> occNameString s == "_"
 #elif defined (GHCLIB_API_810)
   (L _ HsRecField {hsRecFieldArg=(L _ (HsUnboundVar _ _))}) -> True
@@ -165,7 +165,7 @@
 varToStr _ = ""
 
 strToVar :: String -> LHsExpr GhcPs
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 strToVar x = noLoc $ HsVar noExtField (noLoc $ mkRdrUnqual (mkVarOcc x))
 #else
 strToVar x = noLoc $ HsVar noExt (noLoc $ mkRdrUnqual (mkVarOcc x))
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Hs/ExtendInstances.hs b/src/Language/Haskell/GhclibParserEx/GHC/Hs/ExtendInstances.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Hs/ExtendInstances.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Hs/ExtendInstances.hs
@@ -18,9 +18,11 @@
 -- representations rather than the terms themselves, leads to
 -- identical results.
 
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Utils.Outputable
+#  if !defined(GHCLIB_API_900)
 import GHC.Driver.Ppr
+#  endif
 #else
 import Outputable
 #endif
@@ -40,7 +42,7 @@
 -- string representations.
 toStr :: Data a => HsExtendInstances a -> String
 toStr (HsExtendInstances e) =
-#if defined(GHCLIB_API_811)
+#if defined(GHCLIB_API_HEAD)
   showPprUnsafe $ showAstData BlankSrcSpan e
 #else
   showSDocUnsafe $ showAstData BlankSrcSpan e
@@ -58,7 +60,7 @@
 -- Use 'ppr' for 'Show'.
 instance Outputable a => Show (HsExtendInstances a) where
   show (HsExtendInstances e) =
-#if defined(GHCLIB_API_811)
+#if defined(GHCLIB_API_HEAD)
     showPprUnsafe $ ppr e
 #else
     showSDocUnsafe $ ppr e
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Hs/ImpExp.hs b/src/Language/Haskell/GhclibParserEx/GHC/Hs/ImpExp.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Hs/ImpExp.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Hs/ImpExp.hs
@@ -14,7 +14,7 @@
   )
 where
 
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Hs.ImpExp
 import GHC.Types.Name.Reader
 #elif defined (GHCLIB_API_810)
@@ -29,7 +29,7 @@
 isPatSynIE IEPattern{} = True
 isPatSynIE _ = False
 
-#if defined(MIN_VERSION_ghc_lib_parser)
+#if defined (MIN_VERSION_ghc_lib_parser)
 #  if !MIN_VERSION_ghc_lib_parser(1,  0,  0) || MIN_VERSION_ghc_lib_parser(8, 10, 0)
 isImportQualifiedPost :: ImportDeclQualifiedStyle -> Bool
 isImportQualifiedPost QualifiedPost = True
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Pat.hs b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Pat.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Pat.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Pat.hs
@@ -11,12 +11,12 @@
   , isPFieldWildcard, isPWildcard, isPFieldPun, isPatTypeSig, isPBangPat, isPViewPat
  ) where
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs
 #else
 import HsSyn
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Types.SrcLoc
 import GHC.Builtin.Types
 import GHC.Types.Name.Reader
@@ -31,7 +31,7 @@
 #endif
 
 patToStr :: LPat GhcPs -> String
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 patToStr (L _ (ConPat _ (L _ x) (PrefixCon []))) | occNameString (rdrNameOcc x) == "True" = "True"
 patToStr (L _ (ConPat _ (L _ x) (PrefixCon []))) | occNameString (rdrNameOcc x) == "False" = "False"
 patToStr (L _ (ConPat _ (L _ x) (PrefixCon []))) | occNameString (rdrNameOcc x) == "[]" = "[]"
@@ -51,41 +51,41 @@
 strToPat :: String -> LPat GhcPs
 strToPat z
   | z == "True"  =
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
   noLoc $
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
     ConPat noExtField (noLoc true_RDR) (PrefixCon [])
 #else
     ConPatIn (noLoc true_RDR) (PrefixCon [])
 #endif
   | z == "False" =
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
   noLoc $
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
     ConPat noExtField (noLoc false_RDR) (PrefixCon [])
 #else
     ConPatIn (noLoc false_RDR) (PrefixCon [])
 #endif
   | z == "[]"    =
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
   noLoc $
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
     ConPat noExtField (noLoc $ nameRdrName nilDataConName) (PrefixCon [])
 #else
     ConPatIn (noLoc $ nameRdrName nilDataConName) (PrefixCon [])
 #endif
   | otherwise =
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
       noLoc $ VarPat noExtField (noLoc $ mkVarUnqual (fsLit z))
 #else
       VarPat noExt (noLoc $ mkVarUnqual (fsLit z))
 #endif
 
 fromPChar :: LPat GhcPs -> Maybe Char
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 fromPChar (L _ (LitPat _ (HsChar _ x))) = Just x
 #else
 fromPChar (dL -> L _ (LitPat _ (HsChar _ x))) = Just x
@@ -99,7 +99,7 @@
 
 -- Field has a '_' as in '{foo=_} or is punned e.g. '{foo}'.
 isPFieldWildcard :: LHsRecField GhcPs (LPat GhcPs) -> Bool
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 isPFieldWildcard (L _ HsRecField {hsRecFieldArg=L _ WildPat {}}) = True
 isPFieldWildcard (L _ HsRecField {hsRecPun=True}) = True
 isPFieldWildcard (L _ HsRecField {}) = False
@@ -110,7 +110,7 @@
 #endif
 
 isPWildcard :: LPat GhcPs -> Bool
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 isPWildcard (L _ (WildPat _)) = True
 #else
 isPWildcard (dL -> L _ (WildPat _)) = True
@@ -118,7 +118,7 @@
 isPWildcard _ = False
 
 isPFieldPun :: LHsRecField GhcPs (LPat GhcPs) -> Bool
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 isPFieldPun (L _ HsRecField {hsRecPun=True}) = True
 #else
 isPFieldPun (dL -> L _ HsRecField {hsRecPun=True}) = True
@@ -126,7 +126,7 @@
 isPFieldPun _ = False
 
 isPatTypeSig, isPBangPat, isPViewPat :: LPat GhcPs -> Bool
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 isPatTypeSig (L _ SigPat{}) = True; isPatTypeSig _ = False
 isPBangPat (L _ BangPat{}) = True; isPBangPat _ = False
 isPViewPat (L _ ViewPat{}) = True; isPViewPat _ = False
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Types.hs b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Types.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Hs/Types.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Hs/Types.hs
@@ -8,12 +8,12 @@
   , isTyQuasiQuote, isUnboxedTuple
   ) where
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs
 #else
 import HsSyn
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Types.SrcLoc
 #else
 import SrcLoc
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Parser.hs b/src/Language/Haskell/GhclibParserEx/GHC/Parser.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Parser.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Parser.hs
@@ -22,12 +22,15 @@
   )
   where
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs
 #else
 import HsSyn
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD)
+import GHC.Driver.Config
+#endif
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Parser.PostProcess
 import GHC.Driver.Session
 import GHC.Data.StringBuffer
@@ -60,16 +63,20 @@
   where
     location = mkRealSrcLoc (mkFastString "<string>") 1 1
     buffer = stringToStringBuffer str
-    parseState = mkPState flags buffer location
-
-#if defined (GHCLIB_API_811)
+    parseState =
+#if defined (GHCLIB_API_HEAD)
+      initParserState (initParserOpts flags) buffer location
+#else
+      mkPState flags buffer location
+#endif
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 parseModule :: String -> DynFlags -> ParseResult (Located HsModule)
 #else
 parseModule :: String -> DynFlags -> ParseResult (Located (HsModule GhcPs))
 #endif
 parseModule = parse Parser.parseModule
 
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 parseSignature :: String -> DynFlags -> ParseResult (Located HsModule)
 #else
 parseSignature :: String -> DynFlags -> ParseResult (Located (HsModule GhcPs))
@@ -89,12 +96,12 @@
 parseDeclaration = parse Parser.parseDeclaration
 
 parseExpression :: String -> DynFlags -> ParseResult (LHsExpr GhcPs)
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD)
 parseExpression s flags =
   case parse Parser.parseExpression s flags of
     POk s e -> unP (runPV . unECP $ e) s
     PFailed ps -> PFailed ps
-#elif defined (GHCLIB_API_810)
+#elif defined (GHCLIB_API_810) || defined (GHCLIB_API_900)
 parseExpression s flags =
   case parse Parser.parseExpression s flags of
     POk s e -> unP (runECP_P e) s
@@ -118,14 +125,14 @@
 parseType :: String -> DynFlags -> ParseResult (LHsType GhcPs)
 parseType = parse Parser.parseType
 
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 parseHeader :: String -> DynFlags -> ParseResult (Located HsModule)
 #else
 parseHeader :: String -> DynFlags -> ParseResult (Located (HsModule GhcPs))
 #endif
 parseHeader = parse Parser.parseHeader
 
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 parseFile :: String
           -> DynFlags
           -> String
@@ -141,4 +148,9 @@
   where
     location = mkRealSrcLoc (mkFastString filename) 1 1
     buffer = stringToStringBuffer str
-    parseState = mkPState flags buffer location
+    parseState =
+#if defined (GHCLIB_API_HEAD)
+      initParserState (initParserOpts flags) buffer location
+#else
+      mkPState flags buffer location
+#endif
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Settings/Config.hs b/src/Language/Haskell/GhclibParserEx/GHC/Settings/Config.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Settings/Config.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Settings/Config.hs
@@ -11,7 +11,7 @@
   )
 where
 
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Settings.Config
 import GHC.Driver.Session
 import GHC.Utils.Fingerprint
@@ -32,7 +32,7 @@
 
 fakeSettings :: Settings
 fakeSettings = Settings
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)|| defined (GHCLIB_API_810)
   { sGhcNameVersion=ghcNameVersion
   , sFileSettings=fileSettings
   , sTargetPlatform=platform
@@ -49,7 +49,7 @@
   }
 #endif
   where
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)|| defined (GHCLIB_API_810)
     toolSettings = ToolSettings {
       toolSettings_opt_P_fingerprint=fingerprint0
       }
@@ -62,7 +62,7 @@
 #endif
     platform =
       Platform{
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
     -- It doesn't matter what values we write here as these fields are
     -- not referenced for our purposes. However the fields are strict
     -- so we must say something.
@@ -73,13 +73,15 @@
       , platformIsCrossCompiling=False
       , platformLeadingUnderscore=False
       , platformTablesNextToCode=False
+#  if !defined (GHCLIB_API_900)
       , platformConstants=platformConstants
+#  endif
       ,
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD)
         platformWordSize=PW8
       , platformArchOS=ArchOS {archOS_arch=ArchUnknown, archOS_OS=OSUnknown}
-#elif defined (GHCLIB_API_810)
+#elif defined (GHCLIB_API_810) || defined (GHCLIB_API_900)
         platformWordSize=PW8
       , platformMini=PlatformMini {platformMini_arch=ArchUnknown, platformMini_os=OSUnknown}
 #else
@@ -91,7 +93,7 @@
     platformConstants =
       PlatformConstants{pc_DYNAMIC_BY_DEFAULT=False,pc_WORD_SIZE=8}
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)|| defined (GHCLIB_API_810)
 fakeLlvmConfig :: LlvmConfig
 fakeLlvmConfig = LlvmConfig [] []
 #else
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Types/Name/Reader.hs b/src/Language/Haskell/GhclibParserEx/GHC/Types/Name/Reader.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Types/Name/Reader.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Types/Name/Reader.hs
@@ -9,7 +9,7 @@
  )
 where
 
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Types.SrcLoc
 import GHC.Types.Name
 import GHC.Types.Name.Reader
diff --git a/src/Language/Haskell/GhclibParserEx/GHC/Utils/Outputable.hs b/src/Language/Haskell/GhclibParserEx/GHC/Utils/Outputable.hs
--- a/src/Language/Haskell/GhclibParserEx/GHC/Utils/Outputable.hs
+++ b/src/Language/Haskell/GhclibParserEx/GHC/Utils/Outputable.hs
@@ -8,16 +8,18 @@
 )
 where
 
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Utils.Outputable
+#if !defined (GHCLIB_API_900)
 import GHC.Driver.Ppr
+#endif
 #else
 import Outputable
 #endif
 
 unsafePrettyPrint :: Outputable a => a -> String
 unsafePrettyPrint =
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD)
   showPprUnsafe . ppr
 #else
   showSDocUnsafe . ppr
diff --git a/test/Test.hs b/test/Test.hs
--- a/test/Test.hs
+++ b/test/Test.hs
@@ -38,17 +38,19 @@
 import Language.Haskell.GhclibParserEx.GHC.Driver.Session
 import Language.Haskell.GhclibParserEx.GHC.Types.Name.Reader
 
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
 import GHC.Hs
 #else
 import HsSyn
 #endif
-#if defined (GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 import GHC.Types.SrcLoc
 import GHC.Driver.Session
 import GHC.Parser.Lexer
 import GHC.Utils.Outputable
+#  if !defined (GHCLIB_API_900)
 import GHC.Driver.Ppr
+#  endif
 import GHC.Utils.Error
 import GHC.Types.Name.Reader
 import GHC.Types.Name.Occurrence
@@ -66,7 +68,7 @@
 import Bag
 #endif
 
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD)
 showSDocUnsafe :: SDoc -> String
 showSDocUnsafe = showPprUnsafe
 #endif
@@ -100,7 +102,7 @@
       let (wrns, errs) = getMessages s flags
       when (not (null errs) || not (null wrns)) $
         assertFailure (report flags wrns ++ report flags errs)
-#if defined (GHCLIB_API_811) || defined (GHCLIB_API_810)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900) || defined (GHCLIB_API_810)
     PFailed s -> assertFailure (report flags $ snd (getMessages s flags))
 #else
     PFailed _ loc err -> assertFailure (report flags $ unitBag $ mkPlainErrMsg flags loc err)
@@ -160,10 +162,10 @@
         Right flags -> chkParseResult report flags $ parseFile foo flags s
   ]
   where
-    flags = unsafeGlobalDynFlags
+    flags = defaultDynFlags fakeSettings fakeLlvmConfig
     report flags msgs = concat [ showSDoc flags msg | msg <- pprErrMsgBagWithLoc msgs ]
 
-#if defined(GHCLIB_API_811)
+#if defined (GHCLIB_API_HEAD) || defined (GHCLIB_API_900)
 moduleTest :: String -> DynFlags -> (Located HsModule -> IO ()) -> IO ()
 #else
 moduleTest :: String -> DynFlags -> (Located (HsModule GhcPs) -> IO ()) -> IO ()
@@ -344,7 +346,7 @@
         Left msg -> assertFailure msg
         Right flags -> chkParseResult report flags $ parseFile foo flags s
 #if defined (MIN_VERSION_ghc_lib_parser)
-#  if  !MIN_VERSION_ghc_lib_parser(1,  0,  0) || MIN_VERSION_ghc_lib_parser(8, 10, 0)
+#  if !MIN_VERSION_ghc_lib_parser(1,  0,  0) || MIN_VERSION_ghc_lib_parser(8, 10, 0)
   , testCase "ImportQualifiedPost" $ do
       case parseImport "import Foo qualified" (flags `xopt_set` ImportQualifiedPost) of
         POk _ (L _ decl) -> assertBool "expected postpositive" (isImportQualifiedPost . ideclQualified $ decl)
@@ -358,7 +360,7 @@
 #endif
   ]
   where
-    flags = unsafeGlobalDynFlags
+    flags = defaultDynFlags fakeSettings fakeLlvmConfig
     report flags msgs = concat [ showSDoc flags msg | msg <- pprErrMsgBagWithLoc msgs ]
 
 nameTests :: TestTree