diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f0b17d3de..4b73442bf 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -43,20 +43,10 @@ jobs:
       fail-fast: true
       matrix:
         versions:
-          - ghc: '8.2.2'
-            cabal: '2.4'
-            prefix: 'v2-'
-            cabalopts: ''
-            testopts: ''
-          - ghc: '8.4.4'
-            cabal: '2.4'
-            prefix: 'v2-'
-            cabalopts: '-f-embed_data_files'
-            testopts: ''
           - ghc: '8.6.5'
             cabal: '3.2'
             prefix: ''
-            cabalopts: ''
+            cabalopts: '-f-embed_data_files'
             testopts: '--test-option=--hide-successes --test-option=--ansi-tricks=false'
           - ghc: '8.8.4'
             cabal: '3.2'
diff --git a/cabal.project b/cabal.project
index a7bfa540f..b0606c372 100644
--- a/cabal.project
+++ b/cabal.project
@@ -1,5 +1,5 @@
 packages: pandoc.cabal
 tests: True
 flags: +embed_data_files
-constraints: aeson >= 2.0.1.0, transformers >= 0.5.6
+constraints: aeson >= 2.0.1.0
 
diff --git a/pandoc.cabal b/pandoc.cabal
index 3bda8e877..1b6f3a50a 100644
--- a/pandoc.cabal
+++ b/pandoc.cabal
@@ -409,31 +409,27 @@ flag trypandoc
 
 common common-options
   default-language: Haskell2010
-  build-depends:    base         >= 4.9 && < 5
+  build-depends:    base         >= 4.12 && < 5
   ghc-options:      -Wall -fno-warn-unused-do-bind
                     -Wincomplete-record-updates
                     -Wnoncanonical-monad-instances
+                    -Wcpp-undef
+                    -Wincomplete-uni-patterns
+                    -Widentities
+                    -Wpartial-fields
+                    -Wmissing-signatures
+                    -fhide-source-paths
+                    -- -Wmissing-export-lists
 
-  if impl(ghc < 8.6)
-    hs-source-dirs:   prelude
-    other-modules:    Prelude
-    build-depends:    base-compat >= 0.10.5
-    other-extensions: NoImplicitPrelude
+  if impl(ghc >= 8.10)
+    ghc-options:    -Wunused-packages
+
+  if impl(ghc >= 9.0)
+    ghc-options:    -Winvalid-haddock
 
   if os(windows)
     cpp-options:      -D_WINDOWS
 
-  -- Later:
-  -- -Wpartial-fields        (currently used in Powerpoint writer)
-  -- -Wmissing-export-lists  (currently some Odt modules violate this)
-  -- -Wredundant-constraints (problematic if we want to support older base)
-  if impl(ghc >= 8.2)
-    ghc-options:      -Wcpp-undef
-  if impl(ghc >= 8.4)
-    ghc-options:      -Wincomplete-uni-patterns
-                      -Widentities
-                      -fhide-source-paths
-
 common common-executable
   import:           common-options
   build-depends:    pandoc
diff --git a/prelude/Prelude.hs b/prelude/Prelude.hs
deleted file mode 100644
index 2d81ec1ff..000000000
--- a/prelude/Prelude.hs
+++ /dev/null
@@ -1,15 +0,0 @@
-{-# LANGUAGE NoImplicitPrelude #-}
-
--- The intent is that this Prelude provide the API of
--- the base 4.11 Prelude in a way that is portable for
--- all base versions.
-
-module Prelude
-(
-  module Prelude.Compat
-, Semigroup(..)
-)
-where
-
-import Prelude.Compat
-import Data.Semigroup (Semigroup(..))  -- includes (<>)
diff --git a/src/Text/Pandoc/App/CommandLineOptions.hs b/src/Text/Pandoc/App/CommandLineOptions.hs
index 0d3c12c30..759f8ac35 100644
--- a/src/Text/Pandoc/App/CommandLineOptions.hs
+++ b/src/Text/Pandoc/App/CommandLineOptions.hs
@@ -33,10 +33,8 @@ import Data.Bifunctor (second)
 import Data.Char (toLower)
 import Data.List (intercalate, sort, foldl')
 #ifdef _WINDOWS
-#if MIN_VERSION_base(4,12,0)
 import Data.List (isPrefixOf)
 #endif
-#endif
 import Data.Maybe (fromMaybe, isJust)
 import Data.Text (Text)
 import Safe (tailDef)
@@ -1078,7 +1076,6 @@ readMetaValue s
 -- beginning with \\ to \\?\UNC\. -- See #5127.
 normalizePath :: FilePath -> FilePath
 #ifdef _WINDOWS
-#if MIN_VERSION_base(4,12,0)
 normalizePath fp =
   if "\\\\" `isPrefixOf` fp && not ("\\\\?\\" `isPrefixOf` fp)
     then "\\\\?\\UNC\\" ++ drop 2 fp
@@ -1086,6 +1083,3 @@ normalizePath fp =
 #else
 normalizePath = id
 #endif
-#else
-normalizePath = id
-#endif