diff --git a/Web/Authenticate/OAuth.hs b/Web/Authenticate/OAuth.hs
--- a/Web/Authenticate/OAuth.hs
+++ b/Web/Authenticate/OAuth.hs
@@ -485,7 +485,7 @@
 paramEncode :: BS.ByteString -> BS.ByteString
 paramEncode = BS.concatMap escape
   where
-    escape c | isAscii c && (isAlpha c || isDigit c || c `elem` "-._~") = BS.singleton c
+    escape c | isAscii c && (isAlpha c || isDigit c || c `elem` ("-._~" :: String)) = BS.singleton c
              | otherwise = let num = map toUpper $ showHex (ord c) ""
                                oct = '%' : replicate (2 - length num) '0' ++ num
                            in BS.pack oct
diff --git a/authenticate-oauth.cabal b/authenticate-oauth.cabal
--- a/authenticate-oauth.cabal
+++ b/authenticate-oauth.cabal
@@ -1,5 +1,5 @@
 name:            authenticate-oauth
-version:         1.5.1
+version:         1.5.1.1
 license:         BSD3
 license-file:    LICENSE
 author:          Hiromi Ishii