diff --git a/specification/appplatform/resource-manager/Microsoft.AppPlatform/preview/2021-09-01-preview/appplatform.json b/specification/appplatform/resource-manager/Microsoft.AppPlatform/preview/2021-09-01-preview/appplatform.json
index c8b04cbe985e..ff38bf79b376 100644
--- a/specification/appplatform/resource-manager/Microsoft.AppPlatform/preview/2021-09-01-preview/appplatform.json
+++ b/specification/appplatform/resource-manager/Microsoft.AppPlatform/preview/2021-09-01-preview/appplatform.json
@@ -4426,8 +4426,8 @@
           "description": "The mount path of the persistent disk.",
           "type": "string"
         },
-        "readonly": {
-          "description": "Indicates whether the persistent disk is a readonly one.",
+        "readOnly": {
+          "description": "Indicates whether the persistent disk is a readOnly one.",
           "type": "boolean"
         },
         "mountOptions": {