diff --git a/jsonnetfile.lock.json b/jsonnetfile.lock.json
index ca87eab1..76ad6b09 100644
--- a/jsonnetfile.lock.json
+++ b/jsonnetfile.lock.json
@@ -8,7 +8,7 @@
                     "subdir": "contrib/kube-prometheus/jsonnet/kube-prometheus"
                 }
             },
-            "version": "a2cea4ac87d32686a2d5ab189f4e694297cbc305"
+            "version": "04235fdb35f150a46d5aeefd72c995bf864d2a2f"
         },
         {
             "name": "ksonnet",
diff --git a/manifests/prometheus-rules.yaml b/manifests/prometheus-rules.yaml
index a049cf46..673dce1f 100644
--- a/manifests/prometheus-rules.yaml
+++ b/manifests/prometheus-rules.yaml
@@ -961,6 +961,16 @@ spec:
       for: 10m
       labels:
         severity: warning
+    - alert: AlertmanagerMembersInconsistent
+      annotations:
+        message: Alertmanager has not found all other members of the cluster.
+      expr: |
+        alertmanager_cluster_members{job="alertmanager-main"}
+          != on (service)
+        count by (service) (alertmanager_cluster_members{job="alertmanager-main"})
+      for: 5m
+      labels:
+        severity: critical
   - name: general.rules
     rules:
     - alert: TargetDown