diff --git a/collects/mred/private/wx/cocoa/frame.rkt b/collects/mred/private/wx/cocoa/frame.rkt
index c70d89d277..c6d31f78f9 100644
--- a/collects/mred/private/wx/cocoa/frame.rkt
+++ b/collects/mred/private/wx/cocoa/frame.rkt
@@ -549,7 +549,7 @@
 
     (define/public (on-activate on?) (void))
 
-    (define/public (set-icon bm1 bm2 [mode 'both]) (void)) ;; FIXME
+    (define/public (set-icon bm1 [bm2 #f] [mode 'both]) (void)) ;; FIXME
 
     (define/override (call-pre-on-event w e)
       (pre-on-event w e))
diff --git a/collects/mred/private/wx/gtk/frame.rkt b/collects/mred/private/wx/gtk/frame.rkt
index 8c43cf8e9e..d91223e21e 100644
--- a/collects/mred/private/wx/gtk/frame.rkt
+++ b/collects/mred/private/wx/gtk/frame.rkt
@@ -334,7 +334,7 @@
 
     (define big-icon #f)
     (define small-icon #f)
-    (define/public (set-icon bm mask [mode 'both])
+    (define/public (set-icon bm [mask #f] [mode 'both])
       (let ([bm (if mask
 		    (let* ([nbm (make-object bitmap%
 					     (send bm get-width)
diff --git a/collects/mred/private/wx/win32/frame.rkt b/collects/mred/private/wx/win32/frame.rkt
index 712f5ffd4a..8a32696d8f 100644
--- a/collects/mred/private/wx/win32/frame.rkt
+++ b/collects/mred/private/wx/win32/frame.rkt
@@ -527,7 +527,7 @@
   (define small-hicon #f)
   (define big-hicon #f)
 
-  (define/public (set-icon bm mask [mode 'both])
+  (define/public (set-icon bm [mask #f] [mode 'both])
     (let* ([bg-hbitmap
             (let* ([bm (make-object bitmap% (send bm get-width) (send bm get-height))]
                    [dc (make-object bitmap-dc% bm)])