diff --git a/rootfs/etc/s6-overlay/scripts/prometheus-readsb b/rootfs/etc/s6-overlay/scripts/prometheus-readsb
index 79f40d3..7fffe64 100755
--- a/rootfs/etc/s6-overlay/scripts/prometheus-readsb
+++ b/rootfs/etc/s6-overlay/scripts/prometheus-readsb
@@ -9,7 +9,7 @@ if chk_enabled "$PROMETHEUS_ENABLE"; then
         sleep 1
     done
     trap "pkill -P $$ || true; s6wrap --timestamps --prepend=prometheus-readsb --quiet --args echo 'service stopping'; exit 0" SIGTERM SIGINT SIGHUP SIGQUIT
-    echo -e "HTTP/1.1 200 OK\nContent-Type: text/plain\n\n$(cat /run/readsb-prometheus.prom)" | ncat -l 9274 > /dev/null 2>&1 &
+    echo -e "HTTP/1.1 200 OK\nContent-Type: text/plain\n\n$(cat /run/readsb-prometheus.prom)" | ncat -l "${PROMETHEUSPORT:-9274}" > /dev/null 2>&1 &
     wait
 else
     exec sleep infinity