diff --git a/kubernetes_state/datadog_checks/kubernetes_state/kubernetes_state.py b/kubernetes_state/datadog_checks/kubernetes_state/kubernetes_state.py
index 1e922038029e3..addfcfd06533b 100644
--- a/kubernetes_state/datadog_checks/kubernetes_state/kubernetes_state.py
+++ b/kubernetes_state/datadog_checks/kubernetes_state/kubernetes_state.py
@@ -431,6 +431,8 @@ def _create_kubernetes_state_prometheus_instance(self, instance):
             ksm_instance['label_to_hostname'] = 'node'
             clustername = get_clustername()
             if clustername != "":
+                # some cluster names are not valid RFC1123, but as we use them as a hostAlias we want them to be valid.
+                clustername = clustername.replace("_", "-")
                 ksm_instance['label_to_hostname_suffix'] = "-" + clustername
 
         if 'labels_mapper' in ksm_instance and not isinstance(ksm_instance['labels_mapper'], dict):