Index: racket/base.rkt
==================================================================
--- racket/base.rkt
+++ racket/base.rkt
@@ -281,26 +281,31 @@
             (get-ffi-obj
              "IupSetCallback" libiup
              (_fun [handle : _ihandle] [name : _iname/upcase] [callback : _fpointer]
                    -> [callback : _fpointer]))])
     (λ (handle name callback)
-      (let ([callback (function-ptr callback (callback-type 'callback-set! handle name))])
+      (let* ([callback1 (function-ptr callback (callback-type 'callback-set! handle name))]
+             [callback0 (set/pointer! handle name callback1)])
         (registry-set! handle
           (cons
-           callback
-           (remove
-            (set/pointer! handle name callback)
-            (registry handle)
-            ptr-equal?)))))))
+           (cons callback1 callback)
+           ((if callback0
+                (cute filter (λ (it) (not (ptr-equal? (car it) callback0))) <>)
+                identity)
+            (registry handle))))))))
 
 (define callback
   (getter-with-setter
    (get-ffi-obj
     "IupGetCallback" libiup
     (_fun [handle : _ihandle] [name : _iname/upcase]
           -> [callback : _fpointer]
-          -> (cast callback _fpointer (callback-type 'callback handle name))))
+          -> (cond
+               [(assoc callback (registry handle) ptr-equal?)
+                => cdr]
+               [else
+                (cast callback _fpointer (callback-type 'callback handle name))])))
    callback-set!))
 
 ;; Layout functions
 
 (define (make-constructor-procedure proc)