diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog for the [`clash-lib`](http://hackage.haskell.org/package/clash-lib) package
 
+## 0.6.6 *December 11th 2015*
+* New features:
+  * Remove all existing HDL files before generating new ones. This can be disabled by the `-clash-noclean` flag. [#96](https://github.com/clash-lang/clash-compiler/issues/96)
+  * Support for `clash-prelude` 0.10.4
+
 ## 0.6.5 *November 17th 2015*
 * Fixes bugs:
   * Integer literals used as arguments not always properly annotated with their type.
diff --git a/clash-lib.cabal b/clash-lib.cabal
--- a/clash-lib.cabal
+++ b/clash-lib.cabal
@@ -1,5 +1,5 @@
 Name:                 clash-lib
-Version:              0.6.5
+Version:              0.6.6
 Synopsis:             CAES Language for Synchronous Hardware - As a Library
 Description:
   CλaSH (pronounced ‘clash’) is a functional hardware description language that
@@ -91,7 +91,7 @@
                       attoparsec              >= 0.10.4.0,
                       base                    >= 4.8 && < 5,
                       bytestring              >= 0.10.0.2,
-                      clash-prelude           >= 0.10,
+                      clash-prelude           >= 0.10.4,
                       concurrent-supply       >= 0.1.7,
                       containers              >= 0.5.0.0,
                       deepseq                 >= 1.3.0.2,
diff --git a/src/CLaSH/Driver.hs b/src/CLaSH/Driver.hs
--- a/src/CLaSH/Driver.hs
+++ b/src/CLaSH/Driver.hs
@@ -6,6 +6,7 @@
 
 import qualified Control.Concurrent.Supply        as Supply
 import           Control.DeepSeq
+import           Control.Monad                    (when)
 import           Control.Monad.State              (evalState, get)
 import           Data.HashMap.Strict              (HashMap)
 import qualified Data.HashMap.Strict              as HashMap
@@ -117,7 +118,7 @@
                        , takeWhile (/= '.') (name2String $ fst topEntity)
                        , "/"
                        ]
-      prepareDir dir
+      prepareDir (opt_cleanhdl opts) (extension hdlState') dir
       mapM_ (writeHDL hdlState' dir) hdlDocs
       copyDataFiles dir dfiles'
 
@@ -144,17 +145,22 @@
 
 -- | Prepares the directory for writing HDL files. This means creating the
 --   dir if it does not exist and removing all existing .hdl files from it.
-prepareDir :: String -> IO ()
-prepareDir dir = do
+prepareDir :: Bool -- ^ Remove existing HDL files
+           -> String -- ^ File extension of the HDL files.
+           -> String
+           -> IO ()
+prepareDir cleanhdl ext dir = do
   -- Create the dir if needed
   Directory.createDirectoryIfMissing True dir
-  -- Find all .hdl files in the directory
-  files <- Directory.getDirectoryContents dir
-  let to_remove = filter ((==".hdl") . FilePath.takeExtension) files
-  -- Prepend the dirname to the filenames
-  let abs_to_remove = map (FilePath.combine dir) to_remove
-  -- Remove the files
-  mapM_ Directory.removeFile abs_to_remove
+  -- Clean the directory when needed
+  when cleanhdl $ do
+    -- Find all HDL files in the directory
+    files <- Directory.getDirectoryContents dir
+    let to_remove = filter ((==ext) . FilePath.takeExtension) files
+    -- Prepend the dirname to the filenames
+    let abs_to_remove = map (FilePath.combine dir) to_remove
+    -- Remove the files
+    mapM_ Directory.removeFile abs_to_remove
 
 -- | Writes a HDL file to the given directory
 writeHDL :: Backend backend => backend -> FilePath -> (String, Doc) -> IO ()
diff --git a/src/CLaSH/Driver/TopWrapper.hs b/src/CLaSH/Driver/TopWrapper.hs
--- a/src/CLaSH/Driver/TopWrapper.hs
+++ b/src/CLaSH/Driver/TopWrapper.hs
@@ -240,12 +240,11 @@
 
 
 -- | Create a single clock path
-clockPorts :: Maybe (String,String) -> [(String,String)]
+clockPorts :: [(String,String)] -> [(String,String)]
            -> ([(Identifier,Expr)],[String])
-clockPorts inp outp = (inp' ++ outp',clks)
+clockPorts inp outp = (ports,clks)
   where
-    inp'  = maybe [] ((:[]) . (pack *** stringToVar)) inp
-    outp' = map (pack *** stringToVar) outp
+    ports = map (pack *** stringToVar) (inp ++ outp)
     clks  = map snd outp
 
 -- | Generate resets
@@ -289,7 +288,7 @@
 
   return [NetDecl rst (Reset nm r),resetGenDecl]
 
--- | The 'NetListMonad' is an transformer stack with 'IO' at the bottom.
+-- | The 'NetListMonad' is a transformer stack with 'IO' at the bottom.
 -- So we must use 'unsafePerformIO'.
 unsafeRunNetlist :: NetlistMonad a
                  -> a
diff --git a/src/CLaSH/Driver/Types.hs b/src/CLaSH/Driver/Types.hs
--- a/src/CLaSH/Driver/Types.hs
+++ b/src/CLaSH/Driver/Types.hs
@@ -15,4 +15,5 @@
                            , opt_specLimit   :: Int
                            , opt_inlineBelow :: Int
                            , opt_dbgLevel    :: DebugLevel
+                           , opt_cleanhdl    :: Bool
                            }