diff --git a/server/prometheus-service.js b/server/prometheus-service.js
index efd02bd..8b96ebd 100644
--- a/server/prometheus-service.js
+++ b/server/prometheus-service.js
@@ -220,6 +220,7 @@ async function getOverviewMetrics(url, sourceName) {
   const instances = new Map();
 
   const getOrCreate = (metric) => {
+    const originalInstance = metric.instance || 'Unknown';
     const job = metric.job || 'Unknown';
     const token = getServerToken(originalInstance, job, sourceName);