diff --git a/docs/recipes/mirror.md b/docs/recipes/mirror.md
index 950030980..cdaeff225 100644
--- a/docs/recipes/mirror.md
+++ b/docs/recipes/mirror.md
@@ -59,6 +59,8 @@ be configured to use the `filesystem` driver for storage.
 
 The easiest way to run a registry as a pull through cache is to run the official
 Registry image.
+At least, you need to specify `proxy.remoteurl` within `/etc/docker/registry/config.yml`
+as described in the following subsection.
 
 Multiple registry caches can be deployed over the same back-end. A single
 registry cache ensures that concurrent requests do not pull duplicate data,