diff --git a/docs/howto-polygon-archive.md b/docs/howto-polygon-archive.md
index c2fa61dc..d6d61acc 100644
--- a/docs/howto-polygon-archive.md
+++ b/docs/howto-polygon-archive.md
@@ -96,6 +96,7 @@ services:
 
 volumes:
     polygon-archive_data:
+    traefik_letsencrypt:
 ```
 
 Make a Dockerfile in a subfolder. First create a folder and open a new file.