diff --git a/docs/reference/configuration.md b/docs/reference/configuration.md
index 8b38dc1aff..869b8a0e21 100644
--- a/docs/reference/configuration.md
+++ b/docs/reference/configuration.md
@@ -2352,9 +2352,13 @@ can be based on the base sandbox image:
 ```dockerfile
 FROM gemini-cli-sandbox
 
-# Add your custom dependencies or configurations here
+# Add your custom dependencies or configurations here.
+# Note: The base image runs as the non-root 'node' user.
+# You must switch to 'root' to install system packages.
 # For example:
+# USER root
 # RUN apt-get update && apt-get install -y some-package
+# USER node
 # COPY ./my-config /app/my-config
 ```