diff --git a/cndict.cabal b/cndict.cabal
--- a/cndict.cabal
+++ b/cndict.cabal
@@ -2,7 +2,7 @@
 -- documentation, see http://haskell.org/cabal/users-guide/
 
 name:                cndict
-version:             0.6.1
+version:             0.6.2
 synopsis:            Chinese/Mandarin <-> English dictionary, Chinese lexer.
 -- description:
 license:             PublicDomain
diff --git a/src/Data/Chinese/Pinyin.hs b/src/Data/Chinese/Pinyin.hs
--- a/src/Data/Chinese/Pinyin.hs
+++ b/src/Data/Chinese/Pinyin.hs
@@ -35,10 +35,10 @@
 modToneNumber fn txt
   | T.null txt || not (isDigit (T.last txt)) ||
     T.last txt > '5' = txt
-  | Just n <- T.findIndex (`elem` "ae") txt' = modify n
+  | Just n <- T.findIndex (`elem` ("ae"::String)) txt' = modify n
   | Just n <- findStrIndex "ou" txt'         = modify n
   | Just n <- findSecondVowel txt'           = modify n
-  | Just n <- T.findIndex (`elem` "aoeiu") txt' = modify n
+  | Just n <- T.findIndex (`elem` ("aoeiu"::String)) txt' = modify n
   | otherwise = T.init txt
   where
     tone = digitToInt (T.last txt)
@@ -48,7 +48,7 @@
 findSecondVowel :: Text -> Maybe Int
 findSecondVowel = listToMaybe . drop 1 . findIndices isVowel . T.unpack
   where
-    isVowel = (`elem` "aoeiu")
+    isVowel = (`elem` ("aoeiu"::String))
 
 findStrIndex :: Text -> Text -> Maybe Int
 findStrIndex key = worker 0