diff --git a/Network/Mail/Mime.hs b/Network/Mail/Mime.hs
--- a/Network/Mail/Mime.hs
+++ b/Network/Mail/Mime.hs
@@ -38,7 +38,10 @@
 import Data.Bits ((.&.), shiftR)
 import Data.Char (isAscii)
 import Data.Word (Word8)
-import qualified Data.Ascii as A
+import qualified Data.ByteString as S
+import Data.Text (Text)
+import qualified Data.Text as T
+import qualified Data.Text.Encoding as TE
 
 -- | Generates a random sequence of alphanumerics of the given length.
 randomString :: RandomGen d => Int -> d -> (String, d)
@@ -56,15 +59,15 @@
         | otherwise = toEnum $ i + fromEnum '0' - 52
 
 -- | MIME boundary between parts of a message.
-newtype Boundary = Boundary { unBoundary :: String }
+newtype Boundary = Boundary { unBoundary :: Text }
 instance Random Boundary where
     randomR = const random
-    random = first Boundary . randomString 10
+    random = first (Boundary . T.pack) . randomString 10
 
 -- | An entire mail message.
 data Mail = Mail
     { -- | All headers, including to, from subject.
-      mailHeaders :: [(A.Ascii, String)]
+      mailHeaders :: [(S.ByteString, Text)]
     -- | A list of different sets of alternatives. As a concrete example:
     --
     -- > mailParts = [ [textVersion, htmlVersion], [attachment1], [attachment1]]
@@ -83,16 +86,16 @@
 
 -- | A single part of a multipart message.
 data Part = Part
-    { partType :: String -- ^ content type
+    { partType :: Text -- ^ content type
     , partEncoding :: Encoding
     -- | The filename for this part, if it is to be sent with an attachemnt
     -- disposition.
-    , partFilename :: Maybe FilePath
-    , partHeaders :: [(A.Ascii, String)]
+    , partFilename :: Maybe Text
+    , partHeaders :: Headers
     , partContent :: L.ByteString
     }
 
-type Headers = [(A.Ascii, String)]
+type Headers = [(S.ByteString, Text)]
 type Pair = (Headers, Builder)
 
 partToPair :: Part -> Pair
@@ -111,7 +114,8 @@
       $ (case disposition of
             Nothing -> id
             Just fn ->
-                (:) ("Content-Disposition", "attachment; filename=" ++ fn))
+                (:) ("Content-Disposition", "attachment; filename="
+                                            `T.append` fn))
       $ headers
     builder =
         case encoding of
@@ -122,7 +126,7 @@
             QuotedPrintableBinary -> quotedPrintable False content
 
 showPairs :: RandomGen g
-          => String -- ^ multipart type, eg mixed, alternative
+          => Text -- ^ multipart type, eg mixed, alternative
           -> [Pair]
           -> g
           -> (Pair, g)
@@ -133,7 +137,7 @@
   where
     (Boundary b, gen') = random gen
     headers =
-        [ ("Content-Type", concat
+        [ ("Content-Type", T.concat
             [ "multipart/"
             , mtype
             , "; boundary=\""
@@ -169,23 +173,18 @@
         , finalBuilder
         ]
 
-showHeader :: (A.Ascii, String) -> Builder
+showHeader :: (S.ByteString, Text) -> Builder
 showHeader (k, v) = mconcat
-    [ fromByteString $ A.toByteString k
+    [ fromByteString k
     , fromByteString ": "
-    , v''
+    , if needsEncodedWord v then encodedWord v else fromText v
     , fromByteString "\n"
     ]
-  where
-   v' = LT.pack v
-   v'' = if needsEncodedWord v'
-            then encodedWord v'
-            else fromLazyText v'
 
-showBoundPart :: Boundary -> ([(A.Ascii, String)], Builder) -> Builder
+showBoundPart :: Boundary -> (Headers, Builder) -> Builder
 showBoundPart (Boundary b) (headers, content) = mconcat
     [ fromByteString "--"
-    , fromString b
+    , fromText b
     , fromByteString "\n"
     , mconcat $ map showHeader headers
     , fromByteString "\n"
@@ -195,7 +194,7 @@
 showBoundEnd :: Boundary -> Builder
 showBoundEnd (Boundary b) = mconcat
     [ fromByteString "\n--"
-    , fromString b
+    , fromText b
     , fromByteString "--"
     ]
 
@@ -223,16 +222,18 @@
 renderSendMail :: Mail -> IO ()
 renderSendMail = sendmail <=< renderMail'
 
+-- FIXME usage of FilePath below can lead to issues with filename encoding
+
 -- | A simple interface for generating an email with HTML and plain-text
 -- alternatives and some file attachments.
 --
 -- Note that we use lazy IO for reading in the attachment contents.
-simpleMail :: String -- ^ to
-           -> String -- ^ from
-           -> String -- ^ subject
+simpleMail :: Text -- ^ to
+           -> Text -- ^ from
+           -> Text -- ^ subject
            -> LT.Text -- ^ plain body
            -> LT.Text -- ^ HTML body
-           -> [(String, FilePath)] -- ^ content type and path of attachments
+           -> [(Text, FilePath)] -- ^ content type and path of attachments
            -> IO Mail
 simpleMail to from subject plainBody htmlBody attachments = do
     as <- forM attachments $ \(ct, fn) -> do
@@ -251,7 +252,7 @@
             $ LT.encodeUtf8 htmlBody
             ] :
             (map (\(ct, fn, content) ->
-                    [Part ct Base64 (Just fn) [] content]) as)
+                    [Part ct Base64 (Just $ T.pack fn) [] content]) as)
         }
 
 -- | The first parameter denotes whether the input should be treated as text.
@@ -285,13 +286,13 @@
     | x < 10 = fromWord8 $ x + 48
     | otherwise = fromWord8 $ x + 55
 
-needsEncodedWord :: LT.Text -> Bool
-needsEncodedWord = not . LT.all isAscii
+needsEncodedWord :: Text -> Bool
+needsEncodedWord = not . T.all isAscii
 
-encodedWord :: LT.Text -> Builder
+encodedWord :: Text -> Builder
 encodedWord t = mconcat
     [ fromByteString "=?utf-8?Q?"
-    , L.foldl' go mempty $ LT.encodeUtf8 t
+    , S.foldl' go mempty $ TE.encodeUtf8 t
     , fromByteString "?="
     ]
   where
diff --git a/mime-mail.cabal b/mime-mail.cabal
--- a/mime-mail.cabal
+++ b/mime-mail.cabal
@@ -1,5 +1,5 @@
 Name:                mime-mail
-Version:             0.2.0.1
+Version:             0.3.0
 Synopsis:            Compose MIME email messages.
 Description:         This package provides some high-level datatypes for declaring MIME email messages, functions for automatically composing these into bytestrings, and the ability to send bytestrings via the sendmail executable. You can also use any other library you wish to send via different methods, eg directly to SMTP.
 Homepage:            http://github.com/snoyberg/mime-mail
@@ -23,7 +23,6 @@
                  , blaze-builder       >= 0.2.1      && < 0.4
                  , bytestring          >= 0.9.1      && < 0.10
                  , text                >= 0.7        && < 0.12
-                 , ascii               >= 0.0.2      && < 0.1
 
 source-repository head
   type:     git