diff --git a/clientutil/backend.go b/clientutil/backend.go
index c63afa7869527d00bc68381ce402544a1c731873..1f49a7e58d4ef0e51c1bc36369e1399441273ef2 100644
--- a/clientutil/backend.go
+++ b/clientutil/backend.go
@@ -57,6 +57,7 @@ func NewBackend(config *BackendConfig) (Backend, error) {
 	return &shardedClient{
 		baseURL:   u,
 		tlsConfig: tlsConfig,
+		urls:      make(map[string]*url.URL),
 		shards:    make(map[string]*http.Client),
 	}, nil
 }