diff --git a/b9.cabal b/b9.cabal
--- a/b9.cabal
+++ b/b9.cabal
@@ -1,5 +1,5 @@
 name:                b9
-version:             0.5.19
+version:             0.5.20
 
 synopsis:            A tool and library for building virtual machine images.
 
@@ -132,7 +132,7 @@
                     , CPP
   hs-source-dirs:    src/lib
   default-language:  Haskell2010
-  ghc-options:       -with-rtsopts=-N -Wall
+  ghc-options:       -Wall
                      -fwarn-unused-binds -fno-warn-unused-do-bind
   if impl(ghc >= 7.8.2) && impl(ghc <= 7.10)
      ghc-options: -fno-warn-amp
diff --git a/prepare_release.sh b/prepare_release.sh
--- a/prepare_release.sh
+++ b/prepare_release.sh
@@ -9,9 +9,9 @@
 #
 set -eu
 
-cabal clean
-./build_and_test.sh
-./build_haddock.sh
-cabal check
-cabal sdist
+stack clean
+stack build
+stack test
+stack haddock
+stack sdist
 
diff --git a/src/lib/B9/DiskImageBuilder.hs b/src/lib/B9/DiskImageBuilder.hs
--- a/src/lib/B9/DiskImageBuilder.hs
+++ b/src/lib/B9/DiskImageBuilder.hs
@@ -237,15 +237,18 @@
                (show imgType'))
   | otherwise = do
       let (Image imgFile imgFmt imgFs) = dest
+          qemuImgOpts = conversionOptions imgFmt
       dbgL
           (printf
-               "Creating empty raw image '%s' with size %s"
+               "Creating empty raw image '%s' with size %s and options %s"
                imgFile
-               (toQemuSizeOptVal imgSize))
+               (toQemuSizeOptVal imgSize)
+               qemuImgOpts)
       cmd
           (printf
-               "qemu-img create -f %s '%s' '%s'"
+               "qemu-img create -f %s %s '%s' '%s'"
                (imageFileExtension imgFmt)
+               qemuImgOpts
                imgFile
                (toQemuSizeOptVal imgSize))
       case (imgFmt, imgFs) of
@@ -343,8 +346,9 @@
         liftIO (removeFile imgIn)
 
 conversionOptions :: ImageType -> String
-conversionOptions Vmdk = " -o adapter_type=lsilogic "
-conversionOptions _    = " "
+conversionOptions Vmdk  = " -o adapter_type=lsilogic "
+conversionOptions QCow2 = " -o compat=1.1,preallocation=metadata,lazy_refcounts=on "
+conversionOptions _     = " "
 
 toQemuSizeOptVal :: ImageSize -> String
 toQemuSizeOptVal (ImageSize amount u) = show amount ++ case u of