diff --git a/data/api/application-service/definitions/registration.yaml b/data/api/application-service/definitions/registration.yaml
index ce702df0..f5db31e6 100644
--- a/data/api/application-service/definitions/registration.yaml
+++ b/data/api/application-service/definitions/registration.yaml
@@ -19,7 +19,7 @@ properties:
     type: string
     description: A unique, user-defined ID of the application service which will never change.
   url:
-    type: string
+    type: ["null", "string"]
     description: The URL for the application service. May include a path after the domain name. Optionally set to null if no traffic is required.
   as_token:
     type: string