diff --git a/zonedb.rkt b/zonedb.rkt
index 58f5be4..7d7f329 100644
--- a/zonedb.rkt
+++ b/zonedb.rkt
@@ -79,9 +79,14 @@
   (define resource (struct-copy rr resource0 [ttl 0]))
   (define name (rr-name resource))
   (define old-expirymap (hash-ref db name hash))
-  (if (hash-has-key? old-expirymap resource) ;; don't update TTLs if entry exists
-      db
-      (hash-set db name (hash-set old-expirymap resource expiry))))
+  (define old-expiry (hash-ref old-expirymap resource 0))
+  (cond
+   [(infinite-lifetime? old-expiry) ;; don't update TTL: the existing record should live forever
+    db]
+   [(or (infinite-lifetime? expiry) (> expiry old-expiry)) ;; update TTL
+    (hash-set db name (hash-set old-expirymap resource expiry))]
+   [else ;; old record finite-lifetime but expiring after the new expiry: leave it alone
+    db]))
 
 ;; Maybe<CompleteAnswer> CompiledZone -> (values CompiledZone Timers)
 (define (incorporate-complete-answer ans db)