diff --git a/docker/Dockerfile b/docker/Dockerfile
index 60701eb..431b667 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -3,7 +3,10 @@ FROM alpine:3.8
 RUN apk update && apk upgrade
 RUN apk add s6
 
+# NB: From Alpine 3.9 onwards, the versions of nodejs and npm in the
+# standard packageset are fine for Syndicate
 RUN apk add --no-cache nodejs npm --repository http://dl-cdn.alpinelinux.org/alpine/edge/main
+
 RUN npm i -g preserves
 ENV NODE_PATH=/usr/lib/node_modules