diff --git a/syndicate/actor.rkt b/syndicate/actor.rkt
index 35b9e24..67af5ce 100644
--- a/syndicate/actor.rkt
+++ b/syndicate/actor.rkt
@@ -68,7 +68,7 @@
 (require "field.rkt")
 (require "support/counter.rkt")
 
-(struct entity (id name assert retract message sync)
+(struct entity (id name assert retract message sync data)
   #:methods gen:custom-write
   [(define (write-proc e port mode)
      (fprintf port "#<entity:~a:~a>" (entity-id e) (entity-name e)))])
@@ -78,7 +78,8 @@
    #:assert [entity-assert #f]
    #:retract [entity-retract #f]
    #:message [entity-message #f]
-   #:sync [entity-sync #f]))
+   #:sync [entity-sync #f]
+   #:data [entity-data (void)]))
 
 (struct entity-ref (relay target attenuation) #:transparent)
 (define (parse-Ref! r) (if (entity-ref? r) r (error 'parse-Ref! "Expected entity-ref; got ~v" r)))