diff --git a/specification/blueprint/resource-manager/Microsoft.Blueprint/preview/2018-11-01-preview/blueprintDefinition.json b/specification/blueprint/resource-manager/Microsoft.Blueprint/preview/2018-11-01-preview/blueprintDefinition.json
index 43616703c192..8c6cb466a66f 100644
--- a/specification/blueprint/resource-manager/Microsoft.Blueprint/preview/2018-11-01-preview/blueprintDefinition.json
+++ b/specification/blueprint/resource-manager/Microsoft.Blueprint/preview/2018-11-01-preview/blueprintDefinition.json
@@ -972,6 +972,7 @@
         },
         "layout": {
           "type": "object",
+          "readOnly": true,
           "description": "Layout view of the blueprint definition for UI reference."
         }
       },