diff --git a/deploy/charts/cert-manager/values.yaml b/deploy/charts/cert-manager/values.yaml
index 459567725..01169b7c2 100644
--- a/deploy/charts/cert-manager/values.yaml
+++ b/deploy/charts/cert-manager/values.yaml
@@ -420,6 +420,8 @@ webhook:
         protocol: TCP
       - port: 53
         protocol: UDP
+      # On OpenShift and OKD, the Kubernetes API server listens on
+      # port 6443.
       - port: 6443
         protocol: TCP
       to: