diff --git a/zonedb.rkt b/zonedb.rkt
index 1bed798..e4a72ab 100644
--- a/zonedb.rkt
+++ b/zonedb.rkt
@@ -29,7 +29,7 @@
 	 bit-string->zone)
 
 (define-type RelativeSeconds Real)
-(define-type AbsoluteSeconds Nonnegative-Real)
+(define-type AbsoluteSeconds Real)
 (define-predicate absolute-seconds? AbsoluteSeconds)
 
 ;; An InfiniteLifetime is an (infinite-lifetime RelativeSeconds), a
@@ -60,7 +60,7 @@
 
 (: current-inexact-seconds : -> AbsoluteSeconds)
 (define (current-inexact-seconds)
-  (cast (/ (current-inexact-milliseconds) 1000.0) AbsoluteSeconds))
+  (/ (current-inexact-milliseconds) 1000.0))
 
 (: still-valid? : Expiry AbsoluteSeconds -> Boolean)
 (define (still-valid? expiry now)
@@ -304,5 +304,7 @@
       ([ (rr0 :: (t:rr empty-packet)) (= 1) (ttl :: bits 32) (rest :: binary) ]
        (loop ((incorporate-rr #f) (struct-copy rr rr0 [ttl ttl]) db) rest))
       ([ (rr0 :: (t:rr empty-packet)) (= 0) (expirytime :: bits 32) (rest :: binary) ]
-       (define new-ttl (cast (exact-floor (- expirytime now)) Nonnegative-Integer))
-       (loop ((incorporate-rr now) (struct-copy rr rr0 [ttl new-ttl]) db) rest)))))
+       (define new-ttl (exact-floor (- expirytime now)))
+       (if (negative? new-ttl)
+	   (loop db rest)
+	   (loop ((incorporate-rr now) (struct-copy rr rr0 [ttl new-ttl]) db) rest))))))