diff --git a/hledger-lib/Hledger/Data/Journal.hs b/hledger-lib/Hledger/Data/Journal.hs
index f6165a624..80e9af1fa 100644
--- a/hledger-lib/Hledger/Data/Journal.hs
+++ b/hledger-lib/Hledger/Data/Journal.hs
@@ -116,8 +116,8 @@ import Data.Text (Text)
 import qualified Data.Text as T
 import Safe (headMay, headDef, maximumMay, minimumMay)
 import Data.Time.Calendar (Day, addDays, fromGregorian)
+import Data.Time.Clock.POSIX (POSIXTime)
 import Data.Tree (Tree, flatten)
-import System.Time (ClockTime(TOD))
 import Text.Printf (printf)
 
 import Hledger.Utils
@@ -234,7 +234,7 @@ nulljournal = Journal {
   ,jtxns                      = []
   ,jfinalcommentlines         = ""
   ,jfiles                     = []
-  ,jlastreadtime              = TOD 0 0
+  ,jlastreadtime              = 0
   }
 
 journalFilePath :: Journal -> FilePath
@@ -697,7 +697,7 @@ journalReverse j =
     }
 
 -- | Set this journal's last read time, ie when its files were last read.
-journalSetLastReadTime :: ClockTime -> Journal -> Journal
+journalSetLastReadTime :: POSIXTime -> Journal -> Journal
 journalSetLastReadTime t j = j{ jlastreadtime = t }
 
 
diff --git a/hledger-lib/Hledger/Data/Json.hs b/hledger-lib/Hledger/Data/Json.hs
index 8b34e0dbc..0a88ff0b4 100644
--- a/hledger-lib/Hledger/Data/Json.hs
+++ b/hledger-lib/Hledger/Data/Json.hs
@@ -43,7 +43,6 @@ import           Data.Maybe (fromMaybe)
 import qualified Data.Text.Lazy    as TL
 import qualified Data.Text.Lazy.Builder as TB
 import           GHC.Generics (Generic)
-import           System.Time (ClockTime)
 
 import           Hledger.Data.Types
 import           Hledger.Data.Amount (amountsRaw, mixed)
@@ -149,7 +148,6 @@ instance ToJSON PayeeDeclarationInfo
 instance ToJSON Commodity
 instance ToJSON TimeclockCode
 instance ToJSON TimeclockEntry
-instance ToJSON ClockTime
 instance ToJSON Journal
 
 instance ToJSON Account where
diff --git a/hledger-lib/Hledger/Data/Types.hs b/hledger-lib/Hledger/Data/Types.hs
index cc25934d1..372ccb3cf 100644
--- a/hledger-lib/Hledger/Data/Types.hs
+++ b/hledger-lib/Hledger/Data/Types.hs
@@ -39,10 +39,10 @@ import Text.Blaze (ToMarkup(..))
 import qualified Data.Map as M
 import Data.Ord (comparing)
 import Data.Text (Text)
-import Data.Time.Calendar
-import Data.Time.LocalTime
+import Data.Time.Calendar (Day)
+import Data.Time.Clock.POSIX (POSIXTime)
+import Data.Time.LocalTime (LocalTime)
 import Data.Word (Word8)
-import System.Time (ClockTime(..))
 
 import Hledger.Utils.Regex
 
@@ -528,11 +528,9 @@ data Journal = Journal {
                                                                     --   followed by any included files in the order encountered.
                                                                     --   TODO: FilePath is a sloppy type here, don't assume it's a
                                                                     --   real file; values like "", "-", "(string)" can be seen
-  ,jlastreadtime          :: ClockTime                              -- ^ when this journal was last read from its file(s)
+  ,jlastreadtime          :: POSIXTime                              -- ^ when this journal was last read from its file(s)
   } deriving (Eq, Generic)
 
-deriving instance Generic ClockTime
-
 -- | A journal in the process of being parsed, not yet finalised.
 -- The data is partial, and list fields are in reverse order.
 type ParsedJournal = Journal
diff --git a/hledger-lib/Hledger/Read/Common.hs b/hledger-lib/Hledger/Read/Common.hs
index e0e13c2f3..47adea68a 100644
--- a/hledger-lib/Hledger/Read/Common.hs
+++ b/hledger-lib/Hledger/Read/Common.hs
@@ -149,9 +149,9 @@ import qualified Data.Semigroup as Sem
 import Data.Text (Text)
 import qualified Data.Text as T
 import Data.Time.Calendar (Day, addDays, fromGregorianValid, toGregorian)
+import Data.Time.Clock.POSIX (getPOSIXTime)
 import Data.Time.LocalTime (LocalTime(..), TimeOfDay(..))
 import Data.Word (Word8)
-import System.Time (getClockTime)
 import Text.Megaparsec
 import Text.Megaparsec.Char (char, char', digitChar, newline, string)
 import Text.Megaparsec.Char.Lexer (decimal)
@@ -363,7 +363,7 @@ parseAndFinaliseJournal' parser iopts f txt = do
 --
 journalFinalise :: InputOpts -> FilePath -> Text -> ParsedJournal -> ExceptT String IO Journal
 journalFinalise InputOpts{forecast_,auto_,balancingopts_,strict_} f txt pj = do
-    t <- liftIO getClockTime
+    t <- liftIO getPOSIXTime
     d <- liftIO getCurrentDay
     -- Infer and apply canonical styles for each commodity (or throw an error).
     -- This affects transaction balancing/assertions/assignments, so needs to be done early.
diff --git a/hledger-lib/hledger-lib.cabal b/hledger-lib/hledger-lib.cabal
index 20d9e834d..0ac014e4f 100644
--- a/hledger-lib/hledger-lib.cabal
+++ b/hledger-lib/hledger-lib.cabal
@@ -120,7 +120,6 @@ library
     , megaparsec >=7.0.0 && <9.2
     , microlens >=0.4
     , mtl >=2.2.1
-    , old-time
     , parser-combinators >=0.4.0
     , pretty-simple >4 && <5
     , regex-tdfa
@@ -171,7 +170,6 @@ test-suite doctest
     , megaparsec >=7.0.0 && <9.2
     , microlens >=0.4
     , mtl >=2.2.1
-    , old-time
     , parser-combinators >=0.4.0
     , pretty-simple >4 && <5
     , regex-tdfa
@@ -224,7 +222,6 @@ test-suite unittest
     , megaparsec >=7.0.0 && <9.2
     , microlens >=0.4
     , mtl >=2.2.1
-    , old-time
     , parser-combinators >=0.4.0
     , pretty-simple >4 && <5
     , regex-tdfa
diff --git a/hledger-lib/package.yaml b/hledger-lib/package.yaml
index 0e02dde4a..1964a3a1f 100644
--- a/hledger-lib/package.yaml
+++ b/hledger-lib/package.yaml
@@ -54,7 +54,6 @@ dependencies:
 - megaparsec >=7.0.0 && <9.2
 - microlens >=0.4
 - mtl >=2.2.1
-- old-time
 - parser-combinators >=0.4.0
 - pretty-simple >4 && <5
 - regex-tdfa
diff --git a/hledger/Hledger/Cli/Utils.hs b/hledger/Hledger/Cli/Utils.hs
index d6cd96499..12ec27df1 100644
--- a/hledger/Hledger/Cli/Utils.hs
+++ b/hledger/Hledger/Cli/Utils.hs
@@ -24,7 +24,6 @@ module Hledger.Cli.Utils
      readFileStrictly,
      pivotByOpts,
      anonymiseByOpts,
-     utcTimeToClockTime,
      journalSimilarTransaction,
      tests_Cli_Utils,
     )
@@ -37,7 +36,8 @@ import qualified Data.Text as T
 import qualified Data.Text.IO as T
 import qualified Data.Text.Lazy as TL
 import qualified Data.Text.Lazy.IO as TL
-import Data.Time (UTCTime, Day)
+import Data.Time (Day)
+import Data.Time.Clock.POSIX (POSIXTime, utcTimeToPOSIXSeconds)
 import Safe (readMay, headMay)
 import System.Console.CmdArgs
 import System.Directory (getModificationTime, getDirectoryContents, copyFile, doesFileExist)
@@ -45,13 +45,9 @@ import System.Exit
 import System.FilePath ((</>), splitFileName, takeDirectory)
 import System.Info (os)
 import System.Process (readProcessWithExitCode)
-import System.Time (diffClockTimes, TimeDiff(TimeDiff))
 import Text.Printf
 import Text.Regex.TDFA ((=~))
 
-import System.Time (ClockTime(TOD))
-import Data.Time.Clock.POSIX (utcTimeToPOSIXSeconds)
-
 import Hledger.Cli.CliOptions
 import Hledger.Cli.Anon
 import Hledger.Data
@@ -166,26 +162,20 @@ journalFileIsNewer Journal{jlastreadtime=tread} f = do
   mtmod <- maybeFileModificationTime f
   return $
     case mtmod of
-      Just tmod -> diffClockTimes tmod tread > (TimeDiff 0 0 0 0 0 0 0)
+      Just tmod -> tmod > tread
       Nothing   -> False
 
 -- | Get the last modified time of the specified file, if it exists.
-maybeFileModificationTime :: FilePath -> IO (Maybe ClockTime)
+maybeFileModificationTime :: FilePath -> IO (Maybe POSIXTime)
 maybeFileModificationTime f = do
   exists <- doesFileExist f
   if exists
   then do
     utc <- getModificationTime f
-    return $ Just $ utcTimeToClockTime utc
+    return . Just $ utcTimeToPOSIXSeconds utc
   else
     return Nothing
 
-utcTimeToClockTime :: UTCTime -> ClockTime
-utcTimeToClockTime utc = TOD posixsecs picosecs
-  where
-    (posixsecs, frac) = properFraction $ utcTimeToPOSIXSeconds utc
-    picosecs = round $ frac * 1e12
-
 -- | Attempt to open a web browser on the given url, all platforms.
 openBrowserOn :: String -> IO ExitCode
 openBrowserOn u = trybrowsers browsers u
diff --git a/hledger/hledger.cabal b/hledger/hledger.cabal
index e7ece5580..242297f8f 100644
--- a/hledger/hledger.cabal
+++ b/hledger/hledger.cabal
@@ -159,7 +159,6 @@ library
     , math-functions >=0.3.3.0
     , megaparsec >=7.0.0 && <9.2
     , mtl >=2.2.1
-    , old-time
     , process
     , regex-tdfa
     , safe >=0.2
@@ -209,7 +208,6 @@ executable hledger
     , math-functions >=0.3.3.0
     , megaparsec >=7.0.0 && <9.2
     , mtl >=2.2.1
-    , old-time
     , process
     , regex-tdfa
     , safe >=0.2
@@ -260,7 +258,6 @@ test-suite unittest
     , math-functions >=0.3.3.0
     , megaparsec >=7.0.0 && <9.2
     , mtl >=2.2.1
-    , old-time
     , process
     , regex-tdfa
     , safe >=0.2
@@ -310,7 +307,6 @@ benchmark bench
     , math-functions >=0.3.3.0
     , megaparsec >=7.0.0 && <9.2
     , mtl >=2.2.1
-    , old-time
     , process
     , regex-tdfa
     , safe >=0.2
diff --git a/hledger/package.yaml b/hledger/package.yaml
index e16bd2fe0..83905ce25 100644
--- a/hledger/package.yaml
+++ b/hledger/package.yaml
@@ -113,7 +113,6 @@ dependencies:
 - haskeline >=0.6
 - megaparsec >=7.0.0 && <9.2
 - mtl >=2.2.1
-- old-time
 - process
 - regex-tdfa
 - safe >=0.2