diff --git a/assets/prometheus/rules/kube-apiserver.rules b/assets/prometheus/rules/kube-apiserver.rules
index 8d8d1392..c041881a 100644
--- a/assets/prometheus/rules/kube-apiserver.rules
+++ b/assets/prometheus/rules/kube-apiserver.rules
@@ -11,6 +11,8 @@ ALERT K8SApiserverDown
 
 # Some verbs excluded because they are expected to be long-lasting:
 # WATCHLIST is long-poll, CONNECT is `kubectl exec`.
+#
+# apiserver_request_latencies' unit is microseconds
 ALERT K8SApiServerLatency
   IF histogram_quantile(
       0.99,