diff --git a/api.rkt b/api.rkt
index addec05..fb4fdc1 100644
--- a/api.rkt
+++ b/api.rkt
@@ -195,21 +195,24 @@
 		   (set-union u1 u2)
 		   (set-union d1 d2)))
 
-;; DomainName CompleteAnswer -> ListOf<IPv4>
+;; DomainName Maybe<CompleteAnswer> -> SetOf<IPv4>
 (define (extract-addresses name ans)
-  (match-define (complete-answer ns us ds) ans)
-  (define rrs (set->list (set-union ns us ds)))
-  (let loop ((names (list name))
-	     (ips (set))
-	     (seen (set)))
-    (if (null? names)
-	ips
-	(let* ((name (car names))
-	       (records (filter (lambda (rr) (equal? name (rr-name rr))) rrs)))
-	  (if (set-member? seen name)
-	      (loop (cdr names) ips seen)
-	      (let ((a-records (filter (lambda (rr) (equal? 'a (rr-type rr))) records))
-		    (cname-records (filter (lambda (rr) (equal? 'cname (rr-type rr))) records)))
-		(loop (append (map rr-rdata cname-records) (cdr names))
-		      (set-union ips (list->set (map rr-rdata a-records)))
-		      (set-add seen name))))))))
+  (match ans
+    [#f ;; name-error/NXDOMAIN, so definitely no addresses.
+     (set)]
+    [(complete-answer ns us ds)
+     (define rrs (set->list (set-union ns us ds)))
+     (let loop ((names (list name))
+		(ips (set))
+		(seen (set)))
+       (if (null? names)
+	   ips
+	   (let* ((name (car names))
+		  (records (filter (lambda (rr) (equal? name (rr-name rr))) rrs)))
+	     (if (set-member? seen name)
+		 (loop (cdr names) ips seen)
+		 (let ((a-records (filter (lambda (rr) (equal? 'a (rr-type rr))) records))
+		       (cname-records (filter (lambda (rr) (equal? 'cname (rr-type rr))) records)))
+		   (loop (append (map rr-rdata cname-records) (cdr names))
+			 (set-union ips (list->set (map rr-rdata a-records)))
+			 (set-add seen name)))))))]))