diff --git a/api.rkt b/api.rkt
index 4eb972a..616a29f 100644
--- a/api.rkt
+++ b/api.rkt
@@ -37,6 +37,7 @@
 (require "mapping.rkt")
 (require racket/set)
 (require racket/match)
+(require racket-typed-matrix/struct-map)
 
 ;; (These utilities need to be defined ahead of the domain struct
 ;; definition.)
@@ -52,13 +53,10 @@
 ;; www.google.com is represented as '(#"www" #"google" #"com").
 (struct domain (labels downcased-labels)
 	#:transparent
-	#:property prop:equal+hash (list domain=? domain-hash-1/2 domain-hash-1/2))
-
-(require racket-typed-matrix/struct-map)
-(install-struct-mapper! struct:domain
-			(lambda (f seed x)
-			  (let-values (((labels seed) (f (domain-labels x) seed)))
-			    (values (make-domain labels) seed))))
+	#:property prop:equal+hash (list domain=? domain-hash-1/2 domain-hash-1/2)
+	#:property prop:struct-map (lambda (f seed x)
+				     (let-values (((labels seed) (f (domain-labels x) seed)))
+				       (values (make-domain labels) seed))))
 
 ;; A ShortString is a String with length 255 or shorter.