diff --git a/HackageProxy.hs b/HackageProxy.hs
--- a/HackageProxy.hs
+++ b/HackageProxy.hs
@@ -6,7 +6,7 @@
 module HackageProxy where
 
 import           Blaze.ByteString.Builder (fromByteString)
-import           ClassyPrelude
+import           BasicPrelude
 import qualified Codec.Archive.Tar        as Tar
 import           Codec.Compression.GZip   (compress)
 import qualified Data.ByteString          as S
@@ -22,6 +22,10 @@
 import           Network.Wai.Handler.Warp (run)
 import           System.FilePath          (takeExtension)
 import           TweakCabal
+import qualified Data.Text as T
+import qualified Data.HashSet as HashSet
+import Data.Text.Encoding (encodeUtf8)
+import qualified Data.ByteString.Lazy as L
 
 data HackageProxySettings = HackageProxySettings
     { hpsPort     :: Int
@@ -31,9 +35,9 @@
 
 runHackageProxy :: HackageProxySettings -> IO ()
 runHackageProxy HackageProxySettings {..} = do
-    baseReq <- parseUrl $ unpack hpsSource
+    baseReq <- parseUrl $ T.unpack hpsSource
     run hpsPort $ app baseReq
-        { checkStatus = \_ _ -> Nothing
+        { checkStatus = \_ _ _ -> Nothing
         -- Sometimes Hackage can be slow at responding.
         , responseTimeout = Just 30000000
         }
@@ -50,33 +54,33 @@
         (src, _) <- unwrapResumable $ responseBody res
 
         let resStatus = responseStatus res
-            resHeaders = (filter ((`elem` safeResponseHeaders) . fst) (responseHeaders res))
+            resHeaders = (filter ((`HashSet.member` safeResponseHeaders) . fst) (responseHeaders res))
 
         if isTarball res
             then do
-                lbs <- fromChunks <$> lazyConsume (src $= ungzip)
+                lbs <- L.fromChunks <$> lazyConsume (src $= ungzip)
                 entries <- mapEntries tweakEntry $ Tar.read lbs
                 return $ responseLBS resStatus resHeaders (compress $ Tar.write entries)
             else return $ ResponseSource resStatus resHeaders (mapOutput (Chunk . fromByteString) src)
       where
         isTarball res =
-            ".tar.gz" `isSuffixOf` rawPathInfo waiReq
+            ".tar.gz" `S.isSuffixOf` rawPathInfo waiReq
             && responseStatus res == status200
         req = baseReq { path = path baseReq `combine` rawPathInfo' }
         rawPathInfo' =
             case pathInfo waiReq of
-                ["package", stripSuffix ".tar.gz" -> Just packver] | Just package <- mpackage ->
+                ["package", T.stripSuffix ".tar.gz" -> Just packver] | Just package <- mpackage ->
                     encodeUtf8 $ intercalate "/" [package, version, packver ++ ".tar.gz"]
                   where
-                    (stripSuffix "-" -> mpackage, version) = breakOnEnd "-" packver
+                    (T.stripSuffix "-" -> mpackage, version) = breakOnEnd "-" packver
                 _ -> rawPathInfo waiReq
         combine a b
-            | "/" `isSuffixOf` a || "/" `S.isPrefixOf` b = a ++ b
-            | otherwise = concat [a, "/", b]
+            | "/" `S.isSuffixOf` a || "/" `S.isPrefixOf` b = a ++ b
+            | otherwise = mconcat [a, "/", b]
 
     tweakEntry e@(Tar.entryContent -> Tar.NormalFile lbs _)
         | takeExtension (Tar.entryPath e) == ".cabal" = e
-            { Tar.entryContent = Tar.NormalFile lbs' $ length lbs'
+            { Tar.entryContent = Tar.NormalFile lbs' $ L.length lbs'
             }
       where
         lbs' = tweakCabal tcs lbs
@@ -87,7 +91,7 @@
     mapEntries _ (Tar.Fail e) = throwIO e
 
 safeResponseHeaders :: HashSet (CI ByteString)
-safeResponseHeaders = pack
+safeResponseHeaders = HashSet.fromList
     [ "content-type"
     , "etag"
     , "expires"
diff --git a/TweakCabal.hs b/TweakCabal.hs
--- a/TweakCabal.hs
+++ b/TweakCabal.hs
@@ -2,7 +2,13 @@
 {-# LANGUAGE RecordWildCards   #-}
 module TweakCabal where
 
-import           ClassyPrelude
+import           BasicPrelude
+import qualified Data.Set                                    as Set
+import qualified Data.Text                                   as T
+import           Data.Text.Encoding.Error                    (lenientDecode)
+import           Data.Text.Lazy                              (pack, unpack)
+import           Data.Text.Lazy.Encoding                     (decodeUtf8With,
+                                                              encodeUtf8)
 import           Debug.Trace
 import           Distribution.Package
 import           Distribution.PackageDescription
@@ -18,7 +24,7 @@
 tweakCabal :: TweakCabalSettings -> LByteString -> LByteString
 tweakCabal TweakCabalSettings {..} bs = fromMaybe bs $ do
     gpd <-
-        case parsePackageDescription $ unpack $ decodeUtf8 bs of
+        case parsePackageDescription $ unpack $ decodeUtf8With lenientDecode bs of
             ParseFailed _ -> Nothing
             ParseOk _ x -> Just x
     let string = showGenericPackageDescription gpd
@@ -43,7 +49,7 @@
     tweakConstraints = map tweakDependency
 
     tweakDependency orig@(Dependency name'@(PackageName name) _)
-        | pack name `elem` tcsNoBounds = Dependency name' anyVersion
+        | T.pack name `Set.member` tcsNoBounds = Dependency name' anyVersion
         | otherwise = orig
 
     tweakComponents (a, b, c) =
diff --git a/hackage-proxy.cabal b/hackage-proxy.cabal
--- a/hackage-proxy.cabal
+++ b/hackage-proxy.cabal
@@ -1,5 +1,5 @@
 name:                hackage-proxy
-version:             0.1.0.0
+version:             0.2.0.0
 synopsis:            Provide a proxy for Hackage which modifies responses in some way.
 description:         The motivating use case for this is testing packages with newer versions of GHC. In this case, upper bounds on base, process, and a few other packages will often prevent compilation. This proxy will allow you to strip those upper bounds and proceed with compilation. In the future, other features may be added as well, such as package replacement.
 homepage:            http://github.com/snoyberg/hackage-proxy
@@ -16,11 +16,11 @@
   other-modules:       HackageProxy
                        TweakCabal
   build-depends:       base >= 4.5 && < 5
-                     , classy-prelude >= 0.5
+                     , basic-prelude >= 0.3.5
                      , Cabal >= 1.12
                      , wai >=1.3
                      , warp >=1.3
-                     , http-conduit >=1.8
+                     , http-conduit >=1.9
                      , transformers >= 0.2
                      , case-insensitive
                      , conduit >= 0.5
@@ -33,3 +33,5 @@
                      , bytestring >= 0.9
                      , text >= 0.11
                      , optparse-applicative >= 0.5
+                     , containers
+                     , unordered-containers
diff --git a/hackage-proxy.hs b/hackage-proxy.hs
--- a/hackage-proxy.hs
+++ b/hackage-proxy.hs
@@ -1,8 +1,10 @@
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE OverloadedStrings #-}
-import           ClassyPrelude
+import           BasicPrelude
 import           HackageProxy
 import           Options.Applicative
+import qualified Data.Text as T
+import qualified Data.Set as Set
 
 hackageProxySettings :: Parser HackageProxySettings
 hackageProxySettings = HackageProxySettings
@@ -19,7 +21,7 @@
        <> short 'n'
        <> metavar "PACKAGE"
         )))
-    <*> (pack <$> strOption
+    <*> (T.pack <$> strOption
         ( long "source"
        <> help "Hackage source URL we're proxying from"
        <> short 's'
@@ -27,14 +29,14 @@
        <> metavar "URL"
         ))
   where
-    fixNoBounds [] = pack $ words "base process Cabal directory template-haskell"
-    fixNoBounds x = pack $ map pack x
+    fixNoBounds [] = Set.fromList $ words "base process Cabal directory template-haskell"
+    fixNoBounds x = Set.fromList $ map T.pack x
 
 main :: IO ()
 main = do
     hps <- execParser opts
     putStrLn $ "Listening on port: " ++ show (hpsPort hps)
-    putStrLn $ "Dropping bounds for: " ++ unwords (unpack $ hpsNoBounds hps)
+    putStrLn $ "Dropping bounds for: " ++ unwords (Set.toList $ hpsNoBounds hps)
     putStrLn $ "Downloading from: " ++ hpsSource hps
     runHackageProxy hps
   where