diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,3 +1,7 @@
+## 1.2.3.2
+
+* Fix withSinkFileBuilder [#344](https://github.com/snoyberg/conduit/pull/344)
+
 ## 1.2.3.1
 
 * Fix typo in implementation of `withProcess_`
diff --git a/Data/Conduit/Binary.hs b/Data/Conduit/Binary.hs
--- a/Data/Conduit/Binary.hs
+++ b/Data/Conduit/Binary.hs
@@ -652,7 +652,7 @@
   -> m a
 withSinkFileBuilder fp inner =
   withRunInIO $ \run ->
-  IO.withBinaryFile fp IO.ReadMode $ \h ->
+  IO.withBinaryFile fp IO.WriteMode $ \h ->
   run $ inner $ CL.mapM_ (liftIO . BB.hPutBuilder h)
 
 -- | Like 'sinkFileCautious', but uses the @with@ pattern instead of
diff --git a/conduit-extra.cabal b/conduit-extra.cabal
--- a/conduit-extra.cabal
+++ b/conduit-extra.cabal
@@ -1,5 +1,5 @@
 Name:                conduit-extra
-Version:             1.2.3.1
+Version:             1.2.3.2
 Synopsis:            Batteries included conduit: adapters for common libraries.
 Description:
     The conduit package itself maintains relative small dependencies. The purpose of this package is to collect commonly used utility functions wrapping other library dependencies, without depending on heavier-weight dependencies. The basic idea is that this package should only depend on haskell-platform packages and conduit.
@@ -41,7 +41,7 @@
       cpp-options: -DALLOW_UNALIGNED_ACCESS
 
   Build-depends:       base                     >= 4.5          && < 5
-                     , conduit                  >= 1.1          && < 1.3
+                     , conduit                  >= 1.2.8        && < 1.3
 
                      , bytestring               >= 0.10.2
                      , exceptions
diff --git a/test/Data/Conduit/BinarySpec.hs b/test/Data/Conduit/BinarySpec.hs
--- a/test/Data/Conduit/BinarySpec.hs
+++ b/test/Data/Conduit/BinarySpec.hs
@@ -10,6 +10,7 @@
 import Control.Monad.IO.Class
 import Control.Exception (IOException)
 import qualified Data.ByteString.Lazy as L
+import qualified Blaze.ByteString.Builder.ByteString as Blaze
 import Test.Hspec
 import Test.Hspec.QuickCheck
 import qualified Data.IORef as I
@@ -44,6 +45,14 @@
 
         it "write" $ do
             runResourceT $ CB.sourceFile "conduit-extra.cabal" C.$$ CB.sinkFile "tmp"
+            bs1 <- S.readFile "conduit-extra.cabal"
+            bs2 <- S.readFile "tmp"
+            bs2 `shouldBe` bs1
+
+
+        it "write builder (withSinkFileBuilder)" $ do
+            runResourceT $ CB.withSinkFileBuilder "tmp" $ \sink ->
+                CB.sourceFile "conduit-extra.cabal" C.=$= CL.map Blaze.fromByteString C.$$ sink
             bs1 <- S.readFile "conduit-extra.cabal"
             bs2 <- S.readFile "tmp"
             bs2 `shouldBe` bs1