diff --git a/specification/containerservices/resource-manager/Microsoft.ContainerService/stable/2017-08-31/managedClusters.json b/specification/containerservices/resource-manager/Microsoft.ContainerService/stable/2017-08-31/managedClusters.json
index f5cebe669d2c..d2ae30c5015e 100644
--- a/specification/containerservices/resource-manager/Microsoft.ContainerService/stable/2017-08-31/managedClusters.json
+++ b/specification/containerservices/resource-manager/Microsoft.ContainerService/stable/2017-08-31/managedClusters.json
@@ -916,6 +916,7 @@
       "properties": {
         "kubeConfig": {
           "type": "string",
+          "format": "byte",
           "description": "Base64-encoded Kubernetes configuration file."
         }
       },