diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog for the [`clash-ghc`](http://hackage.haskell.org/package/clash-ghc) 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-ghc.cabal b/clash-ghc.cabal
--- a/clash-ghc.cabal
+++ b/clash-ghc.cabal
@@ -1,5 +1,5 @@
 Name:                 clash-ghc
-Version:              0.6.5
+Version:              0.6.6
 Synopsis:             CAES Language for Synchronous Hardware
 Description:
   CλaSH (pronounced ‘clash’) is a functional hardware description language that
@@ -98,7 +98,7 @@
                       clash-systemverilog       >= 0.6.3,
                       clash-vhdl                >= 0.6.4,
                       clash-verilog             >= 0.6.3,
-                      clash-prelude             >= 0.10.3 && < 0.11,
+                      clash-prelude             >= 0.10.4 && < 0.11,
                       ghc-typelits-extra        >= 0.1,
                       ghc-typelits-natnormalise >= 0.3
 
diff --git a/src-bin/Main.hs b/src-bin/Main.hs
--- a/src-bin/Main.hs
+++ b/src-bin/Main.hs
@@ -120,6 +120,7 @@
                              , opt_inlineLimit = 20
                              , opt_specLimit   = 20
                              , opt_inlineBelow = 15
+                             , opt_cleanhdl    = True
                              })
     (argv3, clashFlagWarnings) <- parseCLaSHFlags r argv2
 
diff --git a/src-ghc/CLaSH/GHC/CLaSHFlags.hs b/src-ghc/CLaSH/GHC/CLaSHFlags.hs
--- a/src-ghc/CLaSH/GHC/CLaSHFlags.hs
+++ b/src-ghc/CLaSH/GHC/CLaSHFlags.hs
@@ -33,6 +33,7 @@
   , defFlag "clash-spec-limit" (IntSuffix (liftEwM . setSpecLimit r))
   , defFlag "clash-inline-below" (IntSuffix (liftEwM . setInlineBelow r))
   , defFlag "clash-debug" (SepArg (setDebugLevel r))
+  , defFlag "clash-noclean" (NoArg (liftEwM (setNoClean r)))
   ]
 
 setInlineLimit :: IORef CLaSHOpts
@@ -56,3 +57,6 @@
 setDebugLevel r s = case readMaybe s of
   Just dbgLvl -> liftEwM $ modifyIORef r (\c -> c {opt_dbgLevel = dbgLvl})
   Nothing     -> addWarn (s ++ " is an invalid debug level")
+
+setNoClean :: IORef CLaSHOpts -> IO ()
+setNoClean r = modifyIORef r (\c -> c {opt_cleanhdl = False})
diff --git a/src-ghc/CLaSH/GHC/Evaluator.hs b/src-ghc/CLaSH/GHC/Evaluator.hs
--- a/src-ghc/CLaSH/GHC/Evaluator.hs
+++ b/src-ghc/CLaSH/GHC/Evaluator.hs
@@ -187,6 +187,15 @@
             [intCon] = tyConDataCons intTc
         in  mkApps (Data intCon) [Left (Literal (IntegerLiteral (toInteger (n - 1))))]
       _ -> e
+  | isSubj && nm == "CLaSH.Sized.Vector.length"
+  = case Either.rights args of
+      [LitTy (NumTy n), _] ->
+        let ty' = runFreshM (termType tcm e)
+            (TyConApp intTcNm _) = tyView ty'
+            (Just intTc) = HashMap.lookup intTcNm tcm
+            [intCon] = tyConDataCons intTc
+        in  mkApps (Data intCon) [Left (Literal (IntegerLiteral (toInteger n)))]
+      _ -> e
 
 reduceConstant _ _ e = e