diff --git a/syndicate/pattern.rkt b/syndicate/pattern.rkt
index 0076bb6..263c2b3 100644
--- a/syndicate/pattern.rkt
+++ b/syndicate/pattern.rkt
@@ -138,7 +138,7 @@
 
       [(ctor piece ...)
        (struct-info? (id-value #'ctor))
-       (let-values (((label arity) (struct-label-and-arity #'ctor)))
+       (let-values (((label arity) (struct-label-and-arity #'ctor (length (syntax->list #'(piece ...))))))
          #`(Pattern-DCompound
             (DCompound-rec (CRec '#,label #,arity)
                            (hasheqv #,@(append*