diff --git a/ghcide/src/Development/IDE/Core/FileStore.hs b/ghcide/src/Development/IDE/Core/FileStore.hs
index f396c21ccc0..fb780c94b28 100644
--- a/ghcide/src/Development/IDE/Core/FileStore.hs
+++ b/ghcide/src/Development/IDE/Core/FileStore.hs
@@ -19,7 +19,8 @@ module Development.IDE.Core.FileStore(
     resetInterfaceStore,
     getModificationTimeImpl,
     addIdeGlobal,
-    getFileContentsImpl
+    getFileContentsImpl,
+    getModTime
     ) where
 
 import           Control.Concurrent.STM                       (atomically)
@@ -31,7 +32,6 @@ import           Control.Monad.IO.Class
 import qualified Data.ByteString                              as BS
 import           Data.Either.Extra
 import qualified Data.HashMap.Strict                          as HM
-import           Data.Int                                     (Int64)
 import qualified Data.Map.Strict                              as Map
 import           Data.Maybe
 import qualified Data.Rope.UTF16                              as Rope
diff --git a/ghcide/test/exe/Main.hs b/ghcide/test/exe/Main.hs
index c61a93de62c..2e0daf287ac 100644
--- a/ghcide/test/exe/Main.hs
+++ b/ghcide/test/exe/Main.hs
@@ -101,6 +101,9 @@ import qualified Language.LSP.Types                       as LSP
 import           Data.IORef.Extra                         (atomicModifyIORef_)
 import qualified Development.IDE.Plugin.HLS.GhcIde        as Ghcide
 import           Text.Regex.TDFA                          ((=~))
+import Development.IDE.Core.FileStore (getModTime)
+import Control.Concurrent (threadDelay)
+import Text.Printf (printf)
 
 waitForProgressBegin :: Session ()
 waitForProgressBegin = skipManyTill anyMessage $ satisfyMaybe $ \case
@@ -5464,8 +5467,23 @@ unitTests = do
             actualOrder <- liftIO $ readIORef orderRef
 
             liftIO $ actualOrder @?= reverse [(1::Int)..20]
+     , testCase "timestamps have millisecond resolution" $ do
+         resolution_us <- findResolution_us 1
+         let msg = printf "Timestamps do not have millisecond resolution: %dus" resolution_us
+         assertBool msg (resolution_us <= 1000)
      ]
 
+findResolution_us :: Int -> IO Int
+findResolution_us delay_us | delay_us >= 1000000 = error "Unable to compute timestamp resolution"
+findResolution_us delay_us = withTempFile $ \f -> withTempFile $ \f' -> do
+    writeFile f ""
+    threadDelay delay_us
+    writeFile f' ""
+    t <- getModTime f
+    t' <- getModTime f'
+    if t /= t' then return delay_us else findResolution_us (delay_us * 10)
+
+
 testIde :: IDE.Arguments -> Session () -> IO ()
 testIde arguments session = do
     config <- getConfigFromEnv