diff --git a/cached_downloader.go b/cached_downloader.go
index cd25860..840d53e 100644
--- a/cached_downloader.go
+++ b/cached_downloader.go
@@ -23,7 +23,7 @@ type CachedDownloader interface {
 }
 
 func NoopTransform(source, destination string) (int64, error) {
-	err := os.Rename(source, destination)
+	err := replace(source, destination)
 	if err != nil {
 		return 0, err
 	}
diff --git a/cached_downloader_test.go b/cached_downloader_test.go
index 351cd44..f9fa7a2 100644
--- a/cached_downloader_test.go
+++ b/cached_downloader_test.go
@@ -472,6 +472,9 @@ var _ = Describe("File cache", func() {
 					))
 
 					url, _ = Url.Parse(server.URL() + "/A")
+					// windows timer increments every 15.6ms, without the sleep
+					// A, B & C will sometimes have the same timestamp
+					time.Sleep(16 * time.Millisecond)
 					cache.Fetch(url, "A", NoopTransform, cancelChan)
 				})
 
diff --git a/file_cache.go b/file_cache.go
index f949ae0..792e8cb 100644
--- a/file_cache.go
+++ b/file_cache.go
@@ -80,7 +80,7 @@ func (e *fileCacheEntry) readCloser() (*CachedFile, error) {
 	return readCloser, nil
 }
 
-func (c *FileCache) Add(cacheKey string, sourcePath string, size int64, cachingInfo CachingInfoType) (*CachedFile, error) {
+func (c *FileCache) Add(cacheKey, sourcePath string, size int64, cachingInfo CachingInfoType) (*CachedFile, error) {
 	lock.Lock()
 	defer lock.Unlock()
 
@@ -105,7 +105,7 @@ func (c *FileCache) Add(cacheKey string, sourcePath string, size int64, cachingI
 	uniqueName := fmt.Sprintf("%s-%d-%d", cacheKey, time.Now().UnixNano(), c.seq)
 	cachePath := filepath.Join(c.cachedPath, uniqueName)
 
-	err := os.Rename(sourcePath, cachePath)
+	err := replace(sourcePath, cachePath)
 	if err != nil {
 		return nil, err
 	}
diff --git a/replace.go b/replace.go
new file mode 100644
index 0000000..f9fc404
--- /dev/null
+++ b/replace.go
@@ -0,0 +1,11 @@
+// +build !windows
+
+package cacheddownloader
+
+import "os"
+
+// if you are wondering why we have this function, see `replace'
+// implementation in replace_windows.go
+func replace(src, dst string) error {
+	return os.Rename(src, dst)
+}
diff --git a/replace_windows.go b/replace_windows.go
new file mode 100644
index 0000000..38ccfe4
--- /dev/null
+++ b/replace_windows.go
@@ -0,0 +1,45 @@
+package cacheddownloader
+
+import (
+	"syscall"
+	"unsafe"
+)
+
+// Replaces `dst' with `src' atomically. Under linux we only have to
+// call os.Rename(), on windows os.Rename() will error if the
+// destination exists already. The replace function serves as a
+// unified interface on both platforms.
+func replace(src, dst string) error {
+	kernel32, err := syscall.LoadLibrary("kernel32.dll")
+	if err != nil {
+		return err
+	}
+	defer syscall.FreeLibrary(kernel32)
+	moveFileExUnicode, err := syscall.GetProcAddress(kernel32, "MoveFileExW")
+	if err != nil {
+		return err
+	}
+
+	srcString, err := syscall.UTF16PtrFromString(src)
+	if err != nil {
+		return err
+	}
+
+	dstString, err := syscall.UTF16PtrFromString(dst)
+	if err != nil {
+		return err
+	}
+
+	srcPtr := uintptr(unsafe.Pointer(srcString))
+	dstPtr := uintptr(unsafe.Pointer(dstString))
+
+	MOVEFILE_REPLACE_EXISTING := 0x1
+	flag := uintptr(MOVEFILE_REPLACE_EXISTING)
+
+	_, _, callErr := syscall.Syscall(uintptr(moveFileExUnicode), 3, srcPtr, dstPtr, flag)
+	if callErr != 0 {
+		return callErr
+	}
+
+	return nil
+}
diff --git a/tar_transformer.go b/tar_transformer.go
index 006dbb8..30bbf47 100644
--- a/tar_transformer.go
+++ b/tar_transformer.go
@@ -110,6 +110,7 @@ func transformZipToTar(path, destPath string) (int64, error) {
 	if err != nil {
 		return 0, err
 	}
+	defer dest.Close()
 
 	zr, err := zip.OpenReader(path)
 	if err != nil {
@@ -136,6 +137,11 @@ func transformZipToTar(path, destPath string) (int64, error) {
 		return 0, err
 	}
 
+	err = zr.Close()
+	if err != nil {
+		return 0, err
+	}
+
 	err = os.Remove(path)
 	if err != nil {
 		return 0, err
diff --git a/tar_transformer_windows_test.go b/tar_transformer_windows_test.go
new file mode 100644
index 0000000..537f08d
--- /dev/null
+++ b/tar_transformer_windows_test.go
@@ -0,0 +1,68 @@
+package cacheddownloader_test
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/pivotal-golang/archiver/extractor/test_helper"
+	. "github.com/pivotal-golang/cacheddownloader"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("TarTransformer", func() {
+	var (
+		scratch string
+
+		sourcePath      string
+		destinationPath string
+
+		transformedSize int64
+		transformErr    error
+	)
+
+	archiveFiles := []test_helper.ArchiveFile{
+		{Name: "some-file", Body: "some-contents"},
+	}
+
+	BeforeEach(func() {
+		var err error
+
+		scratch, err = ioutil.TempDir("", "tar-transformer-scratch")
+		Expect(err).ShouldNot(HaveOccurred())
+
+		destinationFile, err := ioutil.TempFile("", "destination")
+		Expect(err).ShouldNot(HaveOccurred())
+
+		err = destinationFile.Close()
+		Expect(err).ShouldNot(HaveOccurred())
+
+		destinationPath = destinationFile.Name()
+	})
+
+	AfterEach(func() {
+		err := os.RemoveAll(scratch)
+		Expect(err).ShouldNot(HaveOccurred())
+	})
+
+	JustBeforeEach(func() {
+		transformedSize, transformErr = TarTransform(sourcePath, destinationPath)
+	})
+
+	Context("when the file is a .zip", func() {
+		BeforeEach(func() {
+			sourcePath = filepath.Join(scratch, "file.zip")
+
+			test_helper.CreateZipArchive(sourcePath, archiveFiles)
+		})
+
+		It("closes the tarfile", func() {
+			// On Windows, you can't remove files that are still open.  On Linux, you can.
+			err := os.Remove(destinationPath)
+
+			Expect(err).ShouldNot(HaveOccurred())
+		})
+	})
+})