diff --git a/splint.cabal b/splint.cabal
--- a/splint.cabal
+++ b/splint.cabal
@@ -1,7 +1,7 @@
 cabal-version: 2.2
 
 name: splint
-version: 1.0.1.0
+version: 1.0.1.1
 
 synopsis: HLint as a GHC source plugin.
 description:
@@ -46,8 +46,10 @@
 
   build-depends:
     base >= 4.12.0 && < 4.15
+    , containers >= 0.6.0 && < 0.7
     , ghc >= 8.6.1 && < 8.11
     , hlint >= 3.0 && < 3.2
+    , stm >= 2.5.0 && < 2.6
   exposed-modules: Splint
   hs-source-dirs: src/lib
   other-modules: Splint.Parser
diff --git a/src/lib/Splint.hs b/src/lib/Splint.hs
--- a/src/lib/Splint.hs
+++ b/src/lib/Splint.hs
@@ -4,7 +4,11 @@
 where
 
 import qualified Bag as GHC
-import qualified Data.IORef as IORef
+import qualified Control.Concurrent as Concurrent
+import qualified Control.Concurrent.STM as Stm
+import qualified Control.Exception as Exception
+import qualified Control.Monad.IO.Class as IO
+import qualified Data.Map as Map
 import qualified ErrUtils as GHC
 import qualified GhcPlugins as GHC
 import qualified Language.Haskell.HLint as HLint
@@ -26,7 +30,7 @@
   (parseFlags, classifies, hint) <- getSettings commandLineOptions
   moduleEx <- Splint.parse parseFlags modSummary hsParsedModule
   dynFlags <- GHC.getDynFlags
-  GHC.liftIO
+  io
     . GHC.printOrThrowWarnings dynFlags
     . GHC.listToBag
     . fmap (ideaToWarnMsg dynFlags)
@@ -36,19 +40,66 @@
 
 type Settings = (HLint.ParseFlags, [HLint.Classify], HLint.Hint)
 
-getSettings :: [GHC.CommandLineOption] -> GHC.Hsc Settings
-getSettings commandLineOptions = GHC.liftIO $ do
-  maybeSettings <- IORef.readIORef settingsRef
-  case maybeSettings of
-    Just settings -> pure settings
-    Nothing -> do
-      settings <- HLint.argsSettings commandLineOptions
-      IORef.writeIORef settingsRef $ Just settings
-      pure settings
+getSettings :: [String] -> GHC.Hsc Settings
+getSettings options = do
+  let insert = Stm.modifyTVar settingsTVar . Map.insert options
+  remoteData <- io . stm $ do
+    settings <- Stm.readTVar settingsTVar
+    let remoteData = Map.findWithDefault NotAsked options settings
+    case remoteData of
+      NotAsked -> insert Loading
+      _ -> pure ()
+    pure remoteData
+  case remoteData of
+    NotAsked -> io . withTMVar settingsTMVar . const $ do
+      result <- Exception.try $ HLint.argsSettings options
+      case result of
+        Left ioException -> do
+          stm . insert $ Failure ioException
+          Exception.throwIO ioException
+        Right settings -> do
+          stm . insert $ Success settings
+          pure settings
+    Loading -> do
+      io $ Concurrent.threadDelay 1000
+      getSettings options
+    Failure ioException -> io $ Exception.throwIO ioException
+    Success settings -> pure settings
 
-{-# NOINLINE settingsRef #-}
-settingsRef :: IORef.IORef (Maybe Settings)
-settingsRef = Unsafe.unsafePerformIO $ IORef.newIORef Nothing
+io :: IO.MonadIO m => IO a -> m a
+io = GHC.liftIO
+
+stm :: Stm.STM a -> IO a
+stm = Stm.atomically
+
+withTMVar :: Stm.TMVar a -> (a -> IO b) -> IO b
+withTMVar var =
+  Exception.bracket (stm $ Stm.takeTMVar var) (stm . Stm.putTMVar var)
+
+-- | Getting settings is not instantaneous. Since settings are usually reused
+-- between modules, it makes sense to cache them. However each module can
+-- potentially customize its settings using the @OPTIONS_GHC@ pragma. This
+-- variable is used as a cache of settings keyed on the command line options.
+settingsTVar
+  :: Stm.TVar (Map.Map [String] (RemoteData Exception.IOException Settings))
+settingsTVar = Unsafe.unsafePerformIO $ Stm.newTVarIO Map.empty
+{-# NOINLINE settingsTVar #-}
+
+-- | Even though we cache settings based on command line options, we only want
+-- to load settings one at a time. Practically this is to work around a bug in
+-- GHC. But aside from that, loading settings calls @withArgs@ and doing that
+-- simultaneously in separate threads is dubious.
+-- <https://gitlab.haskell.org/ghc/ghc/issues/18261>
+settingsTMVar :: Stm.TMVar ()
+settingsTMVar = Unsafe.unsafePerformIO $ Stm.newTMVarIO ()
+{-# NOINLINE settingsTMVar #-}
+
+data RemoteData e a
+  = NotAsked
+  | Loading
+  | Failure e
+  | Success a
+  deriving (Eq, Show)
 
 ideaToWarnMsg :: GHC.DynFlags -> HLint.Idea -> GHC.WarnMsg
 ideaToWarnMsg dynFlags idea =