diff --git a/jsonnet/kube-prometheus/alerts/alertmanager.libsonnet b/jsonnet/kube-prometheus/alerts/alertmanager.libsonnet
index 42ae3f98353e23d5d4dbc527ff3d17b7a4018220..bf58862dd26a16b718a2b3d931faa0ef2819d744 100644
--- a/jsonnet/kube-prometheus/alerts/alertmanager.libsonnet
+++ b/jsonnet/kube-prometheus/alerts/alertmanager.libsonnet
@@ -37,7 +37,7 @@
             },
             expr: |||
               alertmanager_cluster_members{%(alertmanagerSelector)s}
-                != on (service)
+                != on (service) GROUP_LEFT()
               count by (service) (alertmanager_cluster_members{%(alertmanagerSelector)s})
             ||| % $._config,
             'for': '5m',