diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,14 @@
 # Changelog
 
+## [0.15.0.3] - 2026-08-11
+
+### Changed
+
+* Path completers now sort the directory listings they complete from.
+  They previously handed back entries in whatever order the filesystem
+  reported them, so the same completion produced different output on
+  different machines.
+
 ## [0.15.0.2] - 2026-05-15
 
 ### Changed
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/opt-env-conf.cabal b/opt-env-conf.cabal
--- a/opt-env-conf.cabal
+++ b/opt-env-conf.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           opt-env-conf
-version:        0.15.0.2
+version:        0.15.0.3
 synopsis:       Settings parsing for Haskell: command-line arguments, environment variables, and configuration values.
 homepage:       https://github.com/NorfairKing/opt-env-conf#readme
 bug-reports:    https://github.com/NorfairKing/opt-env-conf/issues
diff --git a/src/OptEnvConf/Completer.hs b/src/OptEnvConf/Completer.hs
--- a/src/OptEnvConf/Completer.hs
+++ b/src/OptEnvConf/Completer.hs
@@ -60,6 +60,9 @@
 listIOCompleter :: IO [String] -> Completer
 listIOCompleter act = Completer $ \s -> filterPrefix s . map finalResult <$> act
 
+-- | Complete a file path.
+--
+-- Files come before directories, each in the order of 'listDirRelSorted'.
 filePath :: Completer
 filePath = Completer $ \fp' -> do
   here <- getCurrentDir
@@ -69,11 +72,11 @@
 filePathFromDir :: Path Abs Dir -> String -> FilePath -> FilePath -> IO [CompletionResult]
 filePathFromDir baseDir prefix fp fp' = do
   fmap (filterPrefix fp' . map (addPrefix prefix)) $ do
-    let listDirForgiving d = fromMaybe ([], []) <$> forgivingAbsence (listDirRel d)
+    let listDirForgiving d = fromMaybe ([], []) <$> forgivingAbsence (listDirRelSorted d)
     (dirsFromParentListing, filesFromParentListing) <- case parseSomeDir fp of
       Nothing -> case fp of
         [] -> do
-          (ds, fs) <- listDirRel baseDir
+          (ds, fs) <- listDirRelSorted baseDir
           pure
             ( map fromRelDir $ filter (not . hiddenRel) ds,
               map fromRelFile $ filter (not . hiddenRel) fs
@@ -97,7 +100,7 @@
       Nothing ->
         if fp == "."
           then do
-            (ds, fs) <- listDirRel baseDir
+            (ds, fs) <- listDirRelSorted baseDir
             pure
               ( map fromRelDir ds,
                 map fromRelFile fs
@@ -144,6 +147,9 @@
       | "/" `isSuffixOf` completionResultValue cr = True
       | otherwise = any (`isSuffixOf` completionResultValue cr) exts
 
+-- | Complete a directory path.
+--
+-- Results are in the order of 'listDirRelSorted'.
 directoryPath :: Completer
 directoryPath = Completer $ \fp' -> do
   here <- getCurrentDir
@@ -153,11 +159,11 @@
 directoryPathFromDir :: Path Abs Dir -> String -> FilePath -> FilePath -> IO [CompletionResult]
 directoryPathFromDir baseDir prefix fp fp' = do
   fmap (filterPrefix fp' . map (addPrefix prefix . dirResult)) $ do
-    let listDirForgiving d = fromMaybe ([], []) <$> forgivingAbsence (listDirRel d)
+    let listDirForgiving d = fromMaybe ([], []) <$> forgivingAbsence (listDirRelSorted d)
     dirsFromParentListing <- case parseSomeDir fp of
       Nothing -> case fp of
         [] -> do
-          (ds, _) <- listDirRel baseDir
+          (ds, _) <- listDirRelSorted baseDir
           pure (map fromRelDir $ filter (not . hiddenRel) ds)
         _ -> pure []
       Just (Abs ad) -> do
@@ -178,7 +184,7 @@
       Just (Rel rf) ->
         if fp == "."
           then do
-            (ds, _) <- listDirRel baseDir
+            (ds, _) <- listDirRelSorted baseDir
             pure (map fromRelDir ds)
           else do
             let dir = parent rf
@@ -209,6 +215,17 @@
     { completionResultValue = s,
       completionResultFinality = CompletionNotFinal
     }
+
+-- | 'listDirRel', but sorted.
+--
+-- The filesystem hands back directory entries in an order it is free to
+-- choose, and different filesystems choose differently.
+-- Sorting here, at the only place completion looks at a directory, is what
+-- makes completion output the same everywhere.
+listDirRelSorted :: Path Abs Dir -> IO ([Path Rel Dir], [Path Rel File])
+listDirRelSorted d = do
+  (ds, fs) <- listDirRel d
+  pure (sort ds, sort fs)
 
 hiddenRel :: Path Rel f -> Bool
 hiddenRel p = case toFilePath p of