diff --git a/README.md b/README.md
index 64a7b3f..5c144b5 100644
--- a/README.md
+++ b/README.md
@@ -116,7 +116,7 @@ services:
   synapse-admin:
     ...
     volumes:
-      ./config.json:/app/config.json
+      ./config.json:/app/config.json:ro
     ...
 ```