diff --git a/go/storage/needle_read_write.go b/go/storage/needle_read_write.go
index cf1b3f94e..813f537df 100644
--- a/go/storage/needle_read_write.go
+++ b/go/storage/needle_read_write.go
@@ -16,6 +16,7 @@ const (
 	FlagHasMime             = 0x04
 	FlagHasLastModifiedDate = 0x08
 	FlagHasTtl              = 0x10
+	FlagIsExtendNeedle      = 0x40 	// TODO Reserve: use extent file to save big needle
 	FlagIsChunkManifest     = 0x80
 	LastModifiedBytesLength = 5
 	TtlBytesLength          = 2