diff --git a/collects/mred/private/wx/cocoa/canvas.rkt b/collects/mred/private/wx/cocoa/canvas.rkt
index 7fe6d67ae2..02b2672132 100644
--- a/collects/mred/private/wx/cocoa/canvas.rkt
+++ b/collects/mred/private/wx/cocoa/canvas.rkt
@@ -280,10 +280,13 @@
        (queue-window-refresh-event this  thunk))
 
      (define/public (paint-or-queue-paint)
-       (or (do-canvas-backing-flush #f)
-           (begin
-             (queue-paint)
-             #f)))
+       (cond
+        [is-gl? (do-canvas-backing-flush #f)
+                (queue-paint)
+                #t]
+        [(do-canvas-backing-flush #f) #t]
+        [else (queue-paint)
+              #f]))
 
      (define/public (do-canvas-backing-flush ctx)
        (do-backing-flush this dc (tell NSGraphicsContext currentContext)
diff --git a/collects/mred/private/wx/cocoa/dc.rkt b/collects/mred/private/wx/cocoa/dc.rkt
index cb81eb3e8f..a04391c39a 100644
--- a/collects/mred/private/wx/cocoa/dc.rkt
+++ b/collects/mred/private/wx/cocoa/dc.rkt
@@ -20,6 +20,7 @@
               do-backing-flush))
 
 (import-class NSOpenGLContext)
+(define NSOpenGLCPSwapInterval 222)
 
 (define dc%
   (class backing-dc%
@@ -44,6 +45,14 @@
                                  (define/override (do-swap-buffers)
                                    (tellv gl-ctx flushBuffer))
                                  (super-new)))])
+                   ;; Disable screen sync for GL flushBuffer; otherwise,
+                   ;; flushBuffer can take around 10 msec depending on the timing
+                   ;; of event polling, and that can be bad for examples like gears.
+                   ;; Maybe whether to sync with the screen should be a configuration
+                   ;; option, but I can't tell the difference on my screen.
+                   (tellv gl-ctx setValues: 
+                          #:type (_ptr i _long) 0
+                          forParameter: #:type _int NSOpenGLCPSwapInterval)
                    (set! gl g)
                    g)))))