diff --git a/hosts/monitoring-3/rules.yml b/hosts/monitoring-3/rules.yml
index 2493b04..bb0f5c9 100644
--- a/hosts/monitoring-3/rules.yml
+++ b/hosts/monitoring-3/rules.yml
@@ -87,3 +87,11 @@ groups:
     annotations:
       summary: "GPG {{ $labels.fingerprint }} is expiring soon"
       description: "GPG with fingerprint {{ $labels.fingerprint }} is expiring in less then six weeks"
+  - alert: NadjaTopIPv4ProxyBroken
+    expr: probe_success{job="blackbox_local_http6", target="blog.nadja.top"} != on (target) probe_success{job="blackbox_local_http4", target="blog.nadja.top"}
+    for: 5m
+    labels:
+      severity: critical
+    annotations:
+      summary: "blog.nadja.top unreachable via IPv4"
+      description: "blog.nadja.top unreachable IPv4, but reachable via IPv6"