diff --git a/third_party/sandboxroot/mirror/external.go b/third_party/sandboxroot/mirror/external.go
index 2c8bcdf..7596843 100644
--- a/third_party/sandboxroot/mirror/external.go
+++ b/third_party/sandboxroot/mirror/external.go
@@ -186,10 +186,10 @@
 		log.Printf("  Uploading to %s...", objName)
 		wr := obj.NewWriter(ctx)
 		if _, err := wr.Write(data); err != nil {
-			return fmt.Errorf("Write failed: %w", err)
+			return fmt.Errorf("Write() failed: %w", err)
 		}
 		if err := wr.Close(); err != nil {
-			return fmt.Errorf("Close failed: %w", err)
+			return fmt.Errorf("Close() failed: %w", err)
 		}
 		return nil
 	}