diff --git a/specification/containerservice/resource-manager/Microsoft.ContainerService/stable/2018-03-31/managedClusters.json b/specification/containerservice/resource-manager/Microsoft.ContainerService/stable/2018-03-31/managedClusters.json
index b12567ed2abf..0b00fbf5f352 100644
--- a/specification/containerservice/resource-manager/Microsoft.ContainerService/stable/2018-03-31/managedClusters.json
+++ b/specification/containerservice/resource-manager/Microsoft.ContainerService/stable/2018-03-31/managedClusters.json
@@ -1035,7 +1035,8 @@
       "properties": {
         "name": {
           "type": "string",
-          "description": "Unique name of the agent pool profile in the context of the subscription and resource group."
+          "description": "Unique name of the agent pool profile in the context of the subscription and resource group.",
+          "pattern": "^[a-z][a-z0-9]{0,11}$"
         },
         "count": {
           "type": "integer",