This is actually a duplicate of issue 14792 which has been ignored for over a year by now.
Please see <URL:http://debbugs.gnu.org/cgi/bugreport.cgi?bug=14792#35> for the reason the provided patch (namely discouraging the use of numbers for object properties) is the only one making sense. Here is the rationale in code: object properties are implemented via key-weak hash tables, and weak hash tables will not work with eqv? as equivalence since key-weakness is related to garbage collection which cannot consider anything but eq?-equivalence. scheme@(guile-user)> (define x (make-weak-key-hash-table)) scheme@(guile-user)> (hashv-set! x 100000000000000000000 #t) $6 = #t scheme@(guile-user)> (gc) scheme@(guile-user)> (hashv-ref x 100000000000000000000) $7 = #f Guile and/or Scheme do not store the equivalence relation in the hashtable itself, and user-definable hash functions may establish arbitrary relations regarding key uniqueness that have no clear relation to the object identity used by garbage collection. -- David Kastrup