diff --git a/registry/storage/driver/gcs/gcs.go b/registry/storage/driver/gcs/gcs.go
index abe0b9f6..ad5f9bd6 100644
--- a/registry/storage/driver/gcs/gcs.go
+++ b/registry/storage/driver/gcs/gcs.go
@@ -493,6 +493,9 @@ func (w *writer) Write(p []byte) (int, error) {
 
 // Size returns the number of bytes written to this FileWriter.
 func (w *writer) Size() int64 {
+	if !w.closed {
+		return w.size + int64(w.buffSize)
+	}
 	return w.size
 }