diff --git a/deploy/update.sh b/deploy/update.sh
index 48bcfa7..2fd7f93 100755
--- a/deploy/update.sh
+++ b/deploy/update.sh
@@ -84,19 +84,33 @@ fi
 VHOST_STAMP="$PREFIX/.vhost-applied"
 vhost_now=$(sha256sum "$APP/deploy/nginx-vhost.conf" | cut -d' ' -f1)
 
-site_host=""; app_port="8080"
-# Written by install.sh. Absent on a deployment that predates it, in which case
-# the commands below are a template rather than a copy-paste.
+site_host=""; app_port=""
+# Written by install.sh, and absent on every deployment that predates it --
+# which is the case that most needs the one-time check below, so the port is
+# recovered from the environment file and the vhost found by what it proxies to.
+# Guessing "your-host" instead would have skipped the check on exactly the hosts
+# it was added for.
 if [[ -f "$PREFIX/.deploy-env" ]]; then
   . "$PREFIX/.deploy-env"
   site_host="$SITE_HOST"; app_port="$APP_PORT"
 fi
-installed_vhost="/etc/nginx/conf.d/${site_host:-your-host}.conf"
+if [[ -z "$app_port" && -f "$PREFIX/lembas.env" ]]; then
+  app_port=$(sed -n 's/^LEMBAS_PORT=//p' "$PREFIX/lembas.env" | tail -1)
+fi
+app_port="${app_port:-8080}"
+
+installed_vhost=""
+if [[ -n "$site_host" && -f "/etc/nginx/conf.d/$site_host.conf" ]]; then
+  installed_vhost="/etc/nginx/conf.d/$site_host.conf"
+else
+  installed_vhost=$(grep -ls "proxy_pass http://127.0.0.1:$app_port" \
+                      /etc/nginx/conf.d/*.conf 2>/dev/null | head -1)
+fi
 
 vhost_stale=""
 if [[ -f "$VHOST_STAMP" ]]; then
   [[ "$(cat "$VHOST_STAMP")" != "$vhost_now" ]] && vhost_stale="the template has changed"
-elif [[ -n "$site_host" && -f "$installed_vhost" ]]; then
+elif [[ -n "$installed_vhost" ]]; then
   # First run with this check, so there is no stamp to compare against. Rather
   # than assume what is installed is current -- which is what the unit check
   # does, and would hide exactly the change this was added for -- look for the
@@ -109,7 +123,7 @@ if [[ -n "$vhost_stale" ]]; then
   echo "== nginx vhost ==" >&2
   echo "   $vhost_stale." >&2
   echo "   Review and reinstall it:" >&2
-  echo "     diff $installed_vhost <(sed \\" >&2
+  echo "     diff ${installed_vhost:-/etc/nginx/conf.d/your-host.conf} <(sed \\" >&2
   echo "       -e 's|__SITE_HOST__|${site_host:-your-host}|g' -e 's|__APP_PORT__|$app_port|g' \\" >&2
   echo "       $APP/deploy/nginx-vhost.conf)" >&2
   echo "   Then: sudo nginx -t && sudo systemctl reload nginx" >&2