diff --git a/backend/src/integrations/uptimeKuma.ts b/backend/src/integrations/uptimeKuma.ts
index 7922d50..94ba388 100644
--- a/backend/src/integrations/uptimeKuma.ts
+++ b/backend/src/integrations/uptimeKuma.ts
@@ -86,17 +86,20 @@ export const uptimeKuma: IntegrationAdapter = {
       s.on('monitorList', (list: Record<string, UptimeKumaMonitor>) => {
         for (const m of Object.values(list)) monitors.set(m.id, m)
       })
-      s.on('importantHeartbeatList', (monitorId: number, beats: Heartbeat[]) => {
+      s.on('importantHeartbeatList', (monitorId: number | string, beats: Heartbeat[]) => {
         const latest = beats[beats.length - 1]
-        if (latest) lastHeartbeat.set(monitorId, latest)
+        if (latest) lastHeartbeat.set(Number(monitorId), latest)
       })
       // importantHeartbeatList only contains status-change events, so a monitor
       // that's been continuously up since it was added has no entries there.
       // heartbeatList carries the regular (non-"important") beat history and is
       // sent for every monitor, so it's needed to populate those cases too.
-      s.on('heartbeatList', (monitorId: number, beats: Heartbeat[]) => {
+      // Uptime Kuma's server emits both with the monitor ID as a string (it
+      // iterates monitor object keys), unlike monitorList/heartbeat which use
+      // numeric IDs — coerce so map lookups by numeric monitor.id still hit.
+      s.on('heartbeatList', (monitorId: number | string, beats: Heartbeat[]) => {
         const latest = beats[beats.length - 1]
-        if (latest) lastHeartbeat.set(monitorId, latest)
+        if (latest) lastHeartbeat.set(Number(monitorId), latest)
       })
       s.on('heartbeat', (beat: Heartbeat & { monitorID: number }) => {
         lastHeartbeat.set(beat.monitorID, beat)