diff --git a/collects/mred/private/wx/cocoa/canvas.rkt b/collects/mred/private/wx/cocoa/canvas.rkt
index 551eed0d..7e3d0cdb 100644
--- a/collects/mred/private/wx/cocoa/canvas.rkt
+++ b/collects/mred/private/wx/cocoa/canvas.rkt
@@ -612,6 +612,7 @@
              1)]))
 
      (define/override (enable-window on?)
+       ;; in atomic mode
        (let ([on? (and on? (is-window-enabled?))])
          (let ([w (tell content-cocoa window)])
            (when (ptr-equal? content-cocoa (tell w firstResponder))
diff --git a/collects/mred/private/wx/cocoa/window.rkt b/collects/mred/private/wx/cocoa/window.rkt
index 0c37a04e..dbe29c72 100644
--- a/collects/mred/private/wx/cocoa/window.rkt
+++ b/collects/mred/private/wx/cocoa/window.rkt
@@ -520,9 +520,11 @@
     (define/public (is-window-enabled?)
       enabled?)
     (define/public (enable on?)
-      (set! enabled? on?)
-      (enable-window on?))
+      (atomically
+       (set! enabled? on?)
+       (enable-window on?)))
     (define/public (enable-window on?)
+      ;; in atomic mode
       (void))
 
     (define block-all-mouse-events? #f)