diff --git a/index.go b/index.go
index 1497919..ca34285 100644
--- a/index.go
+++ b/index.go
@@ -78,6 +78,10 @@ type IndexReader interface {
 	Close() error
 }
 
+type IndexReaderBackupable interface {
+	Backup(string) error
+}
+
 type IndexReaderRegexp interface {
 	FieldDictRegexp(field string, regex string) (FieldDict, error)
 }