diff --git a/builder/virtualbox/step_download_iso.go b/builder/virtualbox/step_download_iso.go
index 62a3a8d21..40553dca2 100644
--- a/builder/virtualbox/step_download_iso.go
+++ b/builder/virtualbox/step_download_iso.go
@@ -6,11 +6,7 @@ import (
 	"github.com/mitchellh/multistep"
 	"github.com/mitchellh/packer/builder/common"
 	"github.com/mitchellh/packer/packer"
-	"io"
-	"io/ioutil"
 	"log"
-	"os"
-	"path/filepath"
 	"time"
 )
 
@@ -23,11 +19,9 @@ import (
 //
 // Produces:
 //   iso_path string
-type stepDownloadISO struct {
-	isoCopyDir string
-}
+type stepDownloadISO struct{}
 
-func (s *stepDownloadISO) Run(state map[string]interface{}) multistep.StepAction {
+func (s stepDownloadISO) Run(state map[string]interface{}) multistep.StepAction {
 	cache := state["cache"].(packer.Cache)
 	config := state["config"].(*config)
 	ui := state["ui"].(packer.Ui)
@@ -84,44 +78,10 @@ DownloadWaitLoop:
 		}
 	}
 
-	// VirtualBox is really dumb and can't figure out that the file is an
-	// ISO unless it has a ".iso" extension. We can't modify the cache
-	// filenames so we just do a copy.
-	tempdir, err := ioutil.TempDir("", "packer")
-	if err != nil {
-		state["error"] = fmt.Errorf("Error copying ISO: %s", err)
-		return multistep.ActionHalt
-	}
-	s.isoCopyDir = tempdir
-
-	f, err := os.Create(filepath.Join(tempdir, "image.iso"))
-	if err != nil {
-		state["error"] = fmt.Errorf("Error copying ISO: %s", err)
-		return multistep.ActionHalt
-	}
-	defer f.Close()
-
-	sourceF, err := os.Open(cachePath)
-	if err != nil {
-		state["error"] = fmt.Errorf("Error copying ISO: %s", err)
-		return multistep.ActionHalt
-	}
-	defer sourceF.Close()
-
-	log.Printf("Copying ISO to temp location: %s", tempdir)
-	if _, err := io.Copy(f, sourceF); err != nil {
-		state["error"] = fmt.Errorf("Error copying ISO: %s", err)
-		return multistep.ActionHalt
-	}
-
 	log.Printf("Path to ISO on disk: %s", cachePath)
-	state["iso_path"] = f.Name()
+	state["iso_path"] = cachePath
 
 	return multistep.ActionContinue
 }
 
-func (s *stepDownloadISO) Cleanup(map[string]interface{}) {
-	if s.isoCopyDir != "" {
-		os.RemoveAll(s.isoCopyDir)
-	}
-}
+func (stepDownloadISO) Cleanup(map[string]interface{}) {}
diff --git a/packer/cache.go b/packer/cache.go
index 6f8d14134..9d69f0c56 100644
--- a/packer/cache.go
+++ b/packer/cache.go
@@ -4,6 +4,7 @@ import (
 	"crypto/sha256"
 	"encoding/hex"
 	"path/filepath"
+	"regexp"
 	"sync"
 )
 
@@ -14,6 +15,9 @@ type Cache interface {
 	// Packer guarantees that no other process will write to this file while
 	// the lock is held.
 	//
+	// If the key has an extension (e.g., file.ext), the resulting path
+	// will have that extension as well.
+	//
 	// The cache will block and wait for the lock.
 	Lock(string) string
 
@@ -44,7 +48,7 @@ func (f *FileCache) Lock(key string) string {
 	rw := f.rwLock(hashKey)
 	rw.Lock()
 
-	return filepath.Join(f.CacheDir, hashKey)
+	return f.cachePath(key, hashKey)
 }
 
 func (f *FileCache) Unlock(key string) {
@@ -58,7 +62,7 @@ func (f *FileCache) RLock(key string) (string, bool) {
 	rw := f.rwLock(hashKey)
 	rw.RLock()
 
-	return filepath.Join(f.CacheDir, hashKey), true
+	return f.cachePath(key, hashKey), true
 }
 
 func (f *FileCache) RUnlock(key string) {
@@ -67,6 +71,16 @@ func (f *FileCache) RUnlock(key string) {
 	rw.RUnlock()
 }
 
+func (f *FileCache) cachePath(key string, hashKey string) string {
+	var suffixPattern = regexp.MustCompile(`(\.\w+)$`)
+	matches := suffixPattern.FindStringSubmatch(key)
+	suffix := ""
+	if matches != nil {
+		suffix = matches[0]
+	}
+	return filepath.Join(f.CacheDir, hashKey+suffix)
+}
+
 func (f *FileCache) hashKey(key string) string {
 	sha := sha256.New()
 	sha.Write([]byte(key))
diff --git a/packer/cache_test.go b/packer/cache_test.go
index 1be344ecc..5fe6f50d0 100644
--- a/packer/cache_test.go
+++ b/packer/cache_test.go
@@ -3,6 +3,7 @@ package packer
 import (
 	"io/ioutil"
 	"os"
+	"strings"
 	"testing"
 )
 
@@ -36,19 +37,23 @@ func TestFileCache(t *testing.T) {
 	defer os.RemoveAll(cacheDir)
 
 	cache := &FileCache{CacheDir: cacheDir}
-	path := cache.Lock("foo")
+	path := cache.Lock("foo.iso")
+
+	if !strings.HasSuffix(path, ".iso") {
+		t.Fatalf("path doesn't end with suffix '%s': '%s'", ".iso", path)
+	}
 	err = ioutil.WriteFile(path, []byte("data"), 0666)
 	if err != nil {
 		t.Fatalf("error writing: %s", err)
 	}
 
-	cache.Unlock("foo")
+	cache.Unlock("foo.iso")
 
-	path, ok := cache.RLock("foo")
+	path, ok := cache.RLock("foo.iso")
 	if !ok {
 		t.Fatal("cache says key doesn't exist")
 	}
-	defer cache.RUnlock("foo")
+	defer cache.RUnlock("foo.iso")
 
 	data, err := ioutil.ReadFile(path)
 	if err != nil {