diff --git a/Codec/Archive/Tar/PackAscii.hs b/Codec/Archive/Tar/PackAscii.hs
--- a/Codec/Archive/Tar/PackAscii.hs
+++ b/Codec/Archive/Tar/PackAscii.hs
@@ -6,10 +6,14 @@
   , fromPosixString
   , posixToByteString
   , byteToPosixString
+  , packAscii
   ) where
 
 import Data.ByteString (ByteString)
+import qualified Data.ByteString.Char8 as BS.Char8
 import qualified Data.ByteString.Short as Sh
+import Data.Char
+import GHC.Stack
 import System.IO.Unsafe (unsafePerformIO)
 import "os-string" System.OsString.Posix (PosixString)
 import qualified "os-string" System.OsString.Posix as PS
@@ -26,3 +30,8 @@
 
 byteToPosixString :: ByteString -> PosixString
 byteToPosixString = PS.PosixString . Sh.toShort
+
+packAscii :: HasCallStack => FilePath -> BS.Char8.ByteString
+packAscii xs
+  | all isAscii xs = BS.Char8.pack xs
+  | otherwise = error $ "packAscii: only ASCII inputs are supported, but got " ++ xs
diff --git a/Codec/Archive/Tar/Types.hs b/Codec/Archive/Tar/Types.hs
--- a/Codec/Archive/Tar/Types.hs
+++ b/Codec/Archive/Tar/Types.hs
@@ -187,9 +187,11 @@
 -- | Ownership information for 'GenEntry'.
 data Ownership = Ownership {
     -- | The owner user name. Should be set to @\"\"@ if unknown.
+    -- Must not contain non-ASCII characters.
     ownerName :: String,
 
     -- | The owner group name. Should be set to @\"\"@ if unknown.
+    -- Must not contain non-ASCII characters.
     groupName :: String,
 
     -- | Numeric owner user id. Should be set to @0@ if unknown.
diff --git a/Codec/Archive/Tar/Write.hs b/Codec/Archive/Tar/Write.hs
--- a/Codec/Archive/Tar/Write.hs
+++ b/Codec/Archive/Tar/Write.hs
@@ -61,15 +61,15 @@
 
 putHeader :: Entry -> LBS.ByteString
 putHeader entry =
-     LBS.Char8.pack
-   $ take 148 block
-  ++ putOct 7 checksum
-  ++ ' ' : drop 156 block
+     LBS.fromStrict
+   $ BS.take 148 block
+  <> putOct 7 checksum
+  <> BS.Char8.cons ' ' (BS.drop 156 block)
   where
     block    = putHeaderNoChkSum entry
-    checksum = foldl' (\x y -> x + ord y) 0 block
+    checksum = BS.Char8.foldl' (\x y -> x + ord y) 0 block
 
-putHeaderNoChkSum :: Entry -> String
+putHeaderNoChkSum :: Entry -> BS.ByteString
 putHeaderNoChkSum Entry {
     entryTarPath     = TarPath name prefix,
     entryContent     = content,
@@ -79,40 +79,40 @@
     entryFormat      = format
   } =
 
-  concat
+  BS.concat
     [ putPosixString 100 name
     , putOct       8 permissions
     , putOct       8 $ ownerId ownership
     , putOct       8 $ groupId ownership
     , numField    12 contentSize
     , putOct      12 modTime
-    , replicate    8 ' ' -- dummy checksum
+    , BS.Char8.replicate 8 ' ' -- dummy checksum
     , putChar8       typeCode
     , putPosixString 100 linkTarget
-    ] ++
+    ] <>
   case format of
   V7Format    ->
-      replicate 255 '\NUL'
-  UstarFormat -> concat
+      BS.Char8.replicate 255 '\NUL'
+  UstarFormat -> BS.Char8.concat
     [ putBString   8 ustarMagic
     , putString   32 $ ownerName ownership
     , putString   32 $ groupName ownership
     , putOct       8 deviceMajor
     , putOct       8 deviceMinor
     , putPosixString 155 prefix
-    , replicate   12 '\NUL'
+    , BS.Char8.replicate   12 '\NUL'
     ]
-  GnuFormat -> concat
+  GnuFormat -> BS.Char8.concat
     [ putBString   8 gnuMagic
     , putString   32 $ ownerName ownership
     , putString   32 $ groupName ownership
     , putGnuDev    8 deviceMajor
     , putGnuDev    8 deviceMinor
     , putPosixString 155 prefix
-    , replicate   12 '\NUL'
+    , BS.Char8.replicate   12 '\NUL'
     ]
   where
-    numField :: FieldWidth -> Int64 -> String
+    numField :: FieldWidth -> Int64 -> BS.Char8.ByteString
     numField w n
       | n >= 0 && n < 1 `shiftL` (3 * (w - 1))
       = putOct w n
@@ -133,7 +133,7 @@
     putGnuDev w n = case content of
       CharacterDevice _ _ -> putOct w n
       BlockDevice     _ _ -> putOct w n
-      _                   -> replicate w '\NUL'
+      _                   -> BS.Char8.replicate w '\NUL'
 
 ustarMagic, gnuMagic :: BS.ByteString
 ustarMagic = BS.Char8.pack "ustar\NUL00"
@@ -143,27 +143,27 @@
 
 type FieldWidth = Int
 
-putBString :: FieldWidth -> BS.ByteString -> String
-putBString n s = BS.Char8.unpack (BS.take n s) ++ replicate (n - BS.length s) '\NUL'
+putBString :: FieldWidth -> BS.ByteString -> BS.ByteString
+putBString n s = BS.take n s <> BS.Char8.replicate (n - BS.length s) '\NUL'
 
-putPosixString :: FieldWidth -> PosixString -> String
-putPosixString n s = fromPosixString (PS.take n s) ++ replicate (n - PS.length s) '\NUL'
+putPosixString :: FieldWidth -> PosixString -> BS.ByteString
+putPosixString n s = posixToByteString (PS.take n s) <> BS.Char8.replicate (n - PS.length s) '\NUL'
 
-putString :: FieldWidth -> String -> String
-putString n s = take n s ++ replicate (n - length s) '\NUL'
+putString :: FieldWidth -> String -> BS.ByteString
+putString n s = BS.take n (packAscii s) <> BS.Char8.replicate (n - length s) '\NUL'
 
-{-# SPECIALISE putLarge :: FieldWidth -> Int64 -> String #-}
-putLarge :: (Bits a, Integral a) => FieldWidth -> a -> String
-putLarge n0 x0 = '\x80' : reverse (go (n0-1) x0)
+{-# SPECIALISE putLarge :: FieldWidth -> Int64 -> BS.ByteString #-}
+putLarge :: (Bits a, Integral a) => FieldWidth -> a -> BS.ByteString
+putLarge n0 x0 = BS.Char8.pack $ '\x80' : reverse (go (n0-1) x0)
   where go 0 _ = []
         go n x = chr (fromIntegral (x .&. 0xff)) : go (n-1) (x `shiftR` 8)
 
-putOct :: (Integral a, Show a) => FieldWidth -> a -> String
+putOct :: (Integral a, Show a) => FieldWidth -> a -> BS.ByteString
 putOct n x =
-  let octStr = take (n-1) $ showOct x ""
-   in replicate (n - length octStr - 1) '0'
-   ++ octStr
-   ++ putChar8 '\NUL'
+  let octStr = BS.take (n-1) $ BS.Char8.pack $ showOct x ""
+   in BS.Char8.replicate (n - BS.length octStr - 1) '0'
+   <> octStr
+   <> putChar8 '\NUL'
 
-putChar8 :: Char -> String
-putChar8 c = [c]
+putChar8 :: Char -> BS.ByteString
+putChar8 = BS.Char8.singleton
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,7 @@
+## 0.6.2.0 Bodigrim <andrew.lelechenko@gmail.com> March 2024
+
+  * Fix issues with Unicode support in filenames.
+
 ## 0.6.1.0 Bodigrim <andrew.lelechenko@gmail.com> January 2024
 
   * Support Unicode in filenames (encoded as UTF-8).
diff --git a/tar.cabal b/tar.cabal
--- a/tar.cabal
+++ b/tar.cabal
@@ -1,6 +1,6 @@
 cabal-version:   2.2
 name:            tar
-version:         0.6.1.0
+version:         0.6.2.0
 license:         BSD-3-Clause
 license-file:    LICENSE
 author:          Duncan Coutts <duncan@community.haskell.org>
diff --git a/test/Codec/Archive/Tar/Pack/Tests.hs b/test/Codec/Archive/Tar/Pack/Tests.hs
--- a/test/Codec/Archive/Tar/Pack/Tests.hs
+++ b/test/Codec/Archive/Tar/Pack/Tests.hs
@@ -5,6 +5,7 @@
 
 module Codec.Archive.Tar.Pack.Tests
   ( prop_roundtrip
+  , unit_roundtrip_unicode
   , unit_roundtrip_symlink
   , unit_roundtrip_long_symlink
   , unit_roundtrip_long_filepath
@@ -17,6 +18,7 @@
 import Data.FileEmbed
 import qualified Codec.Archive.Tar as Tar
 import qualified Codec.Archive.Tar.Pack as Pack
+import qualified Codec.Archive.Tar.Read as Read
 import Codec.Archive.Tar.Types (GenEntries(..), Entries, simpleEntry, toTarPath, GenEntry (entryTarPath))
 import qualified Codec.Archive.Tar.Unpack as Unpack
 import qualified Codec.Archive.Tar.Write as Write
@@ -153,3 +155,17 @@
   let tar :: BL.ByteString = BL.fromStrict $(embedFile "test/data/long-symlink.tar")
       entries = Tar.foldEntries (:) [] (const []) (Tar.read tar)
   in Tar.write entries === tar
+
+unit_roundtrip_unicode :: Property
+unit_roundtrip_unicode = do
+  ioProperty $ withSystemTempDirectory "tar-test" $ \baseDir -> do
+    let relFile = "TModula𐐀bA.hs"
+
+    canWriteFile <- try (writeFile (baseDir </> relFile) "foo")
+    case canWriteFile of
+      Left (e :: IOException) -> pure $ property True
+      Right () -> do
+        entries <- Pack.pack baseDir [relFile]
+        pure $ case Tar.foldlEntries (flip seq) () (Read.read (Write.write entries)) of
+          Right{} -> property True
+          Left (err, _) -> counterexample (show err) $ property False
diff --git a/test/Properties.hs b/test/Properties.hs
--- a/test/Properties.hs
+++ b/test/Properties.hs
@@ -66,6 +66,7 @@
     , testGroup "pack" [
       adjustOption (\(QuickCheckMaxRatio n) -> QuickCheckMaxRatio (max n 100)) $
       testProperty "roundtrip" Pack.prop_roundtrip,
+      testProperty "unicode" Pack.unit_roundtrip_unicode,
       testProperty "symlink" Pack.unit_roundtrip_symlink,
       testProperty "long filepath" Pack.unit_roundtrip_long_filepath,
       testProperty "long symlink" Pack.unit_roundtrip_long_symlink