diff --git a/backends/storage.go b/backends/storage.go
index 119ddb6..02e2a57 100644
--- a/backends/storage.go
+++ b/backends/storage.go
@@ -14,6 +14,7 @@ type StorageBackend interface {
 	Get(key string) (Metadata, io.ReadCloser, error)
 	Lock(filename string) (error)
 	Unlock(filename string) (error)
+	CheckLock(filename string) (bool, error)
 	Put(key string, r io.Reader, expiry time.Time, deleteKey, accessKey string, srcIp string) (Metadata, error)
 	PutMetadata(key string, m Metadata) error
 	ServeFile(key string, w http.ResponseWriter, r *http.Request) error
@@ -27,4 +28,3 @@ type MetaStorageBackend interface {
 
 var NotFoundErr = errors.New("File not found.")
 var FileEmptyError = errors.New("Empty file")
-var FileLockedError = errors.New("Locked file")