diff --git a/third_party/sandboxroot/mirror/main.go b/third_party/sandboxroot/mirror/main.go
index 06479d3..a3256ee 100644
--- a/third_party/sandboxroot/mirror/main.go
+++ b/third_party/sandboxroot/mirror/main.go
@@ -28,7 +28,7 @@
 // ourMirrorURL returns a fully formed URL-string to our mirror (as defined by
 // flags), optionally appending the given parts as file path parts.
 func ourMirrorURL(parts ...string) string {
-	u := url.URL{}
+	var u url.URL
 	u.Scheme = "https"
 	u.Host = "storage.googleapis.com"