diff --git a/hledger-lib/Hledger/Data/Account.hs b/hledger-lib/Hledger/Data/Account.hs
index 0e7fadc14..66bd94499 100644
--- a/hledger-lib/Hledger/Data/Account.hs
+++ b/hledger-lib/Hledger/Data/Account.hs
@@ -34,7 +34,10 @@ module Hledger.Data.Account
 
 import qualified Data.HashSet as HS
 import qualified Data.HashMap.Strict as HM
-import Data.List (find, foldl', sortOn)
+import Data.List (find, sortOn)
+#if !MIN_VERSION_base(4,20,0)
+import Data.List (foldl')
+#endif
 import Data.List.Extra (groupOn)
 import qualified Data.Map as M
 import Data.Ord (Down(..))
diff --git a/hledger-lib/Hledger/Data/Amount.hs b/hledger-lib/Hledger/Data/Amount.hs
index 3f8a5e2eb..db7b2a0c6 100644
--- a/hledger-lib/Hledger/Data/Amount.hs
+++ b/hledger-lib/Hledger/Data/Amount.hs
@@ -39,6 +39,7 @@ with similar amounts since it mostly ignores costss and commodity exchange rates
 
 -}
 
+{-# LANGUAGE CPP  #-}
 {-# LANGUAGE OverloadedStrings  #-}
 {-# LANGUAGE RecordWildCards    #-}
 {-# LANGUAGE NamedFieldPuns #-}
@@ -175,7 +176,10 @@ import Data.Char (isDigit)
 import Data.Decimal (DecimalRaw(..), decimalPlaces, normalizeDecimal, roundTo)
 import Data.Default (Default(..))
 import Data.Foldable (toList)
-import Data.List (find, foldl', intercalate, intersperse, mapAccumL, partition)
+import Data.List (find, intercalate, intersperse, mapAccumL, partition)
+#if !MIN_VERSION_base(4,20,0)
+import Data.List (foldl')
+#endif
 import Data.List.NonEmpty (NonEmpty(..), nonEmpty)
 import qualified Data.Map.Strict as M
 import qualified Data.Set as S
diff --git a/hledger-lib/Hledger/Data/Journal.hs b/hledger-lib/Hledger/Data/Journal.hs
index 87fda5196..f6d1d1631 100644
--- a/hledger-lib/Hledger/Data/Journal.hs
+++ b/hledger-lib/Hledger/Data/Journal.hs
@@ -1,9 +1,10 @@
+{-# LANGUAGE CPP                 #-}
 {-# LANGUAGE NamedFieldPuns      #-}
 {-# LANGUAGE OverloadedStrings   #-}
 {-# LANGUAGE Rank2Types          #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections       #-}
-{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE RecordWildCards     #-}
 
 {-|
 
@@ -122,7 +123,10 @@ import Control.Monad.State.Strict (StateT)
 import Data.Char (toUpper, isDigit)
 import Data.Default (Default(..))
 import Data.Foldable (toList)
-import Data.List ((\\), find, foldl', sortBy, union, intercalate)
+import Data.List ((\\), find, sortBy, union, intercalate)
+#if !MIN_VERSION_base(4,20,0)
+import Data.List (foldl')
+#endif
 import Data.List.Extra (nubSort)
 import qualified Data.Map.Strict as M
 import Data.Maybe (catMaybes, fromMaybe, mapMaybe, maybeToList)
diff --git a/hledger-lib/Hledger/Data/Posting.hs b/hledger-lib/Hledger/Data/Posting.hs
index fb9cfed76..4a36c5730 100644
--- a/hledger-lib/Hledger/Data/Posting.hs
+++ b/hledger-lib/Hledger/Data/Posting.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE NamedFieldPuns #-}
 {-|
 
 A 'Posting' represents a change (by some 'MixedAmount') of the balance in
@@ -8,6 +7,8 @@ look up the date or description there.
 
 -}
 
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE OverloadedStrings #-}
 
 module Hledger.Data.Posting (
@@ -82,7 +83,10 @@ import Data.Foldable (asum)
 import Data.Function ((&))
 import qualified Data.Map as M
 import Data.Maybe (fromMaybe, isJust, mapMaybe)
-import Data.List (foldl', sort, union)
+import Data.List (sort, union)
+#if !MIN_VERSION_base(4,20,0)
+import Data.List (foldl')
+#endif
 import qualified Data.Set as S
 import Data.Text (Text)
 import qualified Data.Text as T
diff --git a/hledger-lib/Hledger/Read/RulesReader.hs b/hledger-lib/Hledger/Read/RulesReader.hs
index 3a29b348b..e52c6ad4b 100644
--- a/hledger-lib/Hledger/Read/RulesReader.hs
+++ b/hledger-lib/Hledger/Read/RulesReader.hs
@@ -14,6 +14,7 @@ Most of the code for reading rules files and csv files is in this module.
 -- stack haddock hledger-lib --fast --no-haddock-deps --haddock-arguments='--ignore-all-exports' --open
 
 --- ** language
+{-# LANGUAGE CPP    #-}
 {-# LANGUAGE FlexibleInstances    #-}
 {-# LANGUAGE OverloadedStrings    #-}
 {-# LANGUAGE RecordWildCards      #-}
@@ -52,7 +53,10 @@ import Control.Monad.Trans.Class  (lift)
 import Data.Char                  (toLower, isDigit, isSpace, isAlphaNum, ord)
 import Data.Bifunctor             (first)
 import Data.Functor               ((<&>))
-import Data.List (elemIndex, foldl', mapAccumL, nub, sortOn)
+import Data.List (elemIndex, mapAccumL, nub, sortOn)
+#if !MIN_VERSION_base(4,20,0)
+import Data.List (foldl')
+#endif
 import Data.List.Extra (groupOn)
 import Data.Maybe (catMaybes, fromMaybe, isJust)
 import Data.MemoUgly (memo)
@@ -1325,9 +1329,7 @@ parseAmount rules record currency s =
       ,showRules rules record
       -- ,"the default-currency is: "++fromMaybe "unspecified" (getDirective "default-currency" rules)
       ,"the parse error is:      " <> T.pack (customErrorBundlePretty e)
-      ,"you may need to \
-        \change your amount*, balance*, or currency* rules, \
-        \or add or change your skip rule"
+      ,"you may need to change your amount*, balance*, or currency* rules, or add or change your skip rule"
       ]
 
 -- | Show the values assigned to each journal field.
diff --git a/hledger-lib/Hledger/Utils.hs b/hledger-lib/Hledger/Utils.hs
index 3435dceb1..cd54380a5 100644
--- a/hledger-lib/Hledger/Utils.hs
+++ b/hledger-lib/Hledger/Utils.hs
@@ -3,6 +3,8 @@ Utilities used throughout hledger, or needed low in the module hierarchy.
 These are the bottom of hledger's module graph.
 -}
 
+{-# LANGUAGE CPP #-}
+
 module Hledger.Utils (
 
   -- * Functions
@@ -69,7 +71,10 @@ where
 
 import Data.Char (toLower)
 import Data.List (intersperse)
-import Data.List.Extra (chunksOf, foldl', foldl1', uncons, unsnoc)
+import Data.List.Extra (chunksOf, foldl1', uncons, unsnoc)
+#if !MIN_VERSION_base(4,20,0)
+import Data.List (foldl')
+#endif
 import qualified Data.Set as Set
 import qualified Data.Text as T (pack, unpack)
 import Data.Tree (foldTree, Tree (Node, subForest))
diff --git a/hledger-lib/Hledger/Utils/Regex.hs b/hledger-lib/Hledger/Utils/Regex.hs
index 6e65f115c..5d99b383b 100644
--- a/hledger-lib/Hledger/Utils/Regex.hs
+++ b/hledger-lib/Hledger/Utils/Regex.hs
@@ -1,7 +1,3 @@
-{-# LANGUAGE FlexibleInstances     #-}
-{-# LANGUAGE MultiParamTypeClasses #-}
-{-# LANGUAGE OverloadedStrings     #-}
-{-# LANGUAGE ScopedTypeVariables   #-}
 {-|
 
 Easy regular expression helpers, currently based on regex-tdfa. These should:
@@ -42,6 +38,12 @@ Current limitations:
 
 -}
 
+{-# LANGUAGE CPP                   #-}
+{-# LANGUAGE FlexibleInstances     #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE OverloadedStrings     #-}
+{-# LANGUAGE ScopedTypeVariables   #-}
+
 module Hledger.Utils.Regex (
   -- * Regexp type and constructors
    Regexp(reString)
@@ -66,7 +68,9 @@ import Control.Monad (foldM)
 import Data.Aeson (ToJSON(..), Value(String))
 import Data.Array ((!), elems, indices)
 import Data.Char (isDigit)
+#if !MIN_VERSION_base(4,20,0)
 import Data.List (foldl')
+#endif
 import Data.MemoUgly (memo)
 import Data.Text (Text)
 import qualified Data.Text as T
diff --git a/hledger/Hledger/Cli/Commands/Balance.hs b/hledger/Hledger/Cli/Commands/Balance.hs
index dd80da384..773377abd 100644
--- a/hledger/Hledger/Cli/Commands/Balance.hs
+++ b/hledger/Hledger/Cli/Commands/Balance.hs
@@ -233,6 +233,7 @@ Currently, empty cells show 0.
 
 -}
 
+{-# LANGUAGE CPP                  #-}
 {-# LANGUAGE OverloadedStrings    #-}
 {-# LANGUAGE NamedFieldPuns       #-}
 {-# LANGUAGE RecordWildCards      #-}
@@ -272,7 +273,10 @@ import Control.Monad (guard)
 import Data.Decimal (roundTo)
 import Data.Default (def)
 import Data.Function (on)
-import Data.List (find, transpose, foldl')
+import Data.List (find, transpose)
+#if !MIN_VERSION_base(4,20,0)
+import Data.List (foldl')
+#endif
 import qualified Data.Map as Map
 import qualified Data.Set as S
 import Data.Maybe (mapMaybe, fromMaybe)
diff --git a/hledger/Hledger/Cli/Commands/Rewrite.hs b/hledger/Hledger/Cli/Commands/Rewrite.hs
index 0fa4f35b2..816fa3d13 100644
--- a/hledger/Hledger/Cli/Commands/Rewrite.hs
+++ b/hledger/Hledger/Cli/Commands/Rewrite.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP               #-}
 {-# LANGUAGE DeriveTraversable #-}
 {-# LANGUAGE LambdaCase        #-}
 {-# LANGUAGE OverloadedStrings #-}
@@ -11,7 +12,10 @@ module Hledger.Cli.Commands.Rewrite (
 where
 
 import Data.Functor.Identity
-import Data.List (sortOn, foldl')
+import Data.List (sortOn)
+#if !MIN_VERSION_base(4,20,0)
+import Data.List (foldl')
+#endif
 import Data.Text (Text)
 import qualified Data.Text as T
 import qualified Data.Text.IO as T
diff --git a/hledger/Hledger/Cli/CompoundBalanceCommand.hs b/hledger/Hledger/Cli/CompoundBalanceCommand.hs
index 2a5a59ac3..7d99a76d3 100644
--- a/hledger/Hledger/Cli/CompoundBalanceCommand.hs
+++ b/hledger/Hledger/Cli/CompoundBalanceCommand.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE RecordWildCards   #-}
 {-# LANGUAGE LambdaCase #-}
@@ -14,7 +15,9 @@ module Hledger.Cli.CompoundBalanceCommand (
  ,compoundBalanceCommand
 ) where
 
+#if !MIN_VERSION_base(4,20,0)
 import Data.List (foldl')
+#endif
 import Data.Maybe (fromMaybe, mapMaybe)
 import qualified Data.Text as T
 import qualified Data.Text.Lazy as TL