diff --git a/collects/mred/private/wx/cocoa/canvas.rkt b/collects/mred/private/wx/cocoa/canvas.rkt
index c7052e65..b18587ed 100644
--- a/collects/mred/private/wx/cocoa/canvas.rkt
+++ b/collects/mred/private/wx/cocoa/canvas.rkt
@@ -79,6 +79,8 @@
 
     (define canvas-style style)
 
+    (define is-visible? #f)
+
     ;; Avoid multiple queued paints:
     (define paint-queued? #f)
     ;; To handle paint requests that happen while on-paint
@@ -92,13 +94,14 @@
         (set! paint-queued? #t)
         (queue-window-event this (lambda () 
                                    (set! paint-queued? #f)
-                                   (set! now-drawing? #t)
-                                   (fix-dc)
-                                   (on-paint)
-                                   (set! now-drawing? #f)
-                                   (when refresh-after-drawing?
-                                     (set! refresh-after-drawing? #f)
-                                     (refresh))))))
+                                   (when is-visible?
+                                     (set! now-drawing? #t)
+                                     (fix-dc)
+                                     (on-paint)
+                                     (set! now-drawing? #f)
+                                     (when refresh-after-drawing?
+                                       (set! refresh-after-drawing? #f)
+                                       (refresh)))))))
     (define/override (refresh)
       (tellv content-cocoa setNeedsDisplay: #:type _BOOL #t))
 
@@ -148,6 +151,11 @@
 
     (define tr 0)
 
+    (define/override (show on?)
+      (set! is-visible? on?)
+      ;; FIXME: what if we're in the middle of an on-paint?
+      (super show on?))
+
     (define/private (do-set-size x y w h)
       (super set-size x y w h)
       (when tr
diff --git a/collects/mred/private/wx/gtk/frame.rkt b/collects/mred/private/wx/gtk/frame.rkt
index 12b08123..8e3c0ecb 100644
--- a/collects/mred/private/wx/gtk/frame.rkt
+++ b/collects/mred/private/wx/gtk/frame.rkt
@@ -128,11 +128,11 @@
                [fh (unbox h-box)])
           (set-top-position (if (or (eq? dir 'both)
                                     (eq? dir 'horizontal))
-                                (/ (- sw fw) 2)
+                                (quotient (- sw fw) 2)
                                 -11111)
                             (if (or (eq? dir 'both)
                                     (eq? dir 'vertical))
-                                (/ (- sh fh) 2)
+                                (quotient (- sh fh) 2)
                                 -11111)))))
 
     (define/override (set-top-position x y)