diff --git a/deploy/bike_admin.service b/deploy/bike_admin.service
index 3a1ce98..fc320f0 100644
--- a/deploy/bike_admin.service
+++ b/deploy/bike_admin.service
@@ -21,6 +21,10 @@ NoNewPrivileges=true
 PrivateTmp=true
 ProtectSystem=full
 ProtectHome=true
+# App data lives next to the checkout at /opt/bike_admin/data (created by the
+# app on startup). systemd requires the ReadWritePaths target to exist before
+# it starts the service, so pre-create it with:
+#   sudo install -d -o bike -g bike /opt/bike_admin/data
 ReadWritePaths=/opt/bike_admin/data
 
 [Install]
diff --git a/deploy/env.production.example b/deploy/env.production.example
index ac2cd12..e762e11 100644
--- a/deploy/env.production.example
+++ b/deploy/env.production.example
@@ -22,4 +22,4 @@ BIKE_ADMIN_BIND_PORT=8000
 # BIKE_ADMIN_SERVICE_DUE_SOON_MILES=200   # service "book soon" lead time
 # BIKE_ADMIN_RENEWAL_DUE_SOON_DAYS=60     # MOT/insurance "due soon" lead time
 # BIKE_ADMIN_RENEWAL_MONTHS=12            # MOT/insurance validity (months)
-# BIKE_ADMIN_DATA_DIR=/opt/bike_admin/data
+# BIKE_ADMIN_DATA_DIR=/opt/bike_admin/data  # (defaults to <WorkingDirectory>/data; matches the systemd unit)