diff --git a/docs/user-guide/configmap/index.md b/docs/user-guide/configmap/index.md
index 7f5377be79..49399cde0e 100644
--- a/docs/user-guide/configmap/index.md
+++ b/docs/user-guide/configmap/index.md
@@ -604,3 +604,5 @@ Kubelet only supports use of ConfigMap for pods it gets from the API server.  Th
 created using kubectl, or indirectly via a replication controller.  It does not include pods created
 via the Kubelet's `--manifest-url` flag, its `--config` flag, or its REST API (these are not common
 ways to create pods.)
+
+NOTE: The key-value optional:true is supported for Kubernetes 1.6 and above.