diff --git a/backend/src/integrations/uptimeKuma.ts b/backend/src/integrations/uptimeKuma.ts
index 2ef162e..7922d50 100644
--- a/backend/src/integrations/uptimeKuma.ts
+++ b/backend/src/integrations/uptimeKuma.ts
@@ -90,6 +90,14 @@ export const uptimeKuma: IntegrationAdapter = {
         const latest = beats[beats.length - 1]
         if (latest) lastHeartbeat.set(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[]) => {
+        const latest = beats[beats.length - 1]
+        if (latest) lastHeartbeat.set(monitorId, latest)
+      })
       s.on('heartbeat', (beat: Heartbeat & { monitorID: number }) => {
         lastHeartbeat.set(beat.monitorID, beat)
       })