diff --git a/collects/mred/private/wx/cocoa/frame.rkt b/collects/mred/private/wx/cocoa/frame.rkt
index b9570d2508..7e464a58a3 100644
--- a/collects/mred/private/wx/cocoa/frame.rkt
+++ b/collects/mred/private/wx/cocoa/frame.rkt
@@ -545,5 +545,6 @@
    ;; in atomic mode
    (for ([b (in-hash-values all-windows)])
      (let ([f (weak-box-value b)])
-       (send f fixup-locations-children)))))
+       (when f
+         (send f fixup-locations-children))))))