diff --git a/collects/mred/private/wx/cocoa/frame.rkt b/collects/mred/private/wx/cocoa/frame.rkt
index 5b6e305ab2..701ed6aabb 100644
--- a/collects/mred/private/wx/cocoa/frame.rkt
+++ b/collects/mred/private/wx/cocoa/frame.rkt
@@ -469,20 +469,24 @@
 
     (define/override (center dir wrt)
       (let ([f (tell #:type _NSRect cocoa frame)]
-            [s (tell #:type _NSRect (tell cocoa screen) frame)])
+            [w (if wrt
+                   (tell #:type _NSRect (send wrt get-cocoa) frame)
+                   (tell #:type _NSRect (tell cocoa screen) frame))])
         (tellv cocoa setFrame: 
                #:type _NSRect (make-NSRect (make-NSPoint 
                                             (if (or (eq? dir 'both)
                                                     (eq? dir 'horizontal))
-                                                (quotient (- (NSSize-width (NSRect-size s))
-                                                             (NSSize-width (NSRect-size f)))
-                                                          2)
+                                                (+ (quotient (- (NSSize-width (NSRect-size w))
+                                                                (NSSize-width (NSRect-size f)))
+                                                             2)
+                                                   (NSPoint-x (NSRect-origin w)))
                                                 (NSPoint-x (NSRect-origin f)))
                                             (if (or (eq? dir 'both)
                                                     (eq? dir 'vertical))
-                                                (quotient (- (NSSize-height (NSRect-size s))
-                                                             (NSSize-height (NSRect-size f)))
-                                                          2)
+                                                (+ (quotient (- (NSSize-height (NSRect-size w))
+                                                                (NSSize-height (NSRect-size f)))
+                                                             2)
+                                                   (NSPoint-y (NSRect-origin w)))
                                                 (NSPoint-x (NSRect-origin f))))
                                            (NSRect-size f))
                display: #:type _BOOL #t)))
diff --git a/collects/mred/private/wxtop.rkt b/collects/mred/private/wxtop.rkt
index 05513e8427..3dba64fd54 100644
--- a/collects/mred/private/wxtop.rkt
+++ b/collects/mred/private/wxtop.rkt
@@ -90,7 +90,7 @@
        [panel #f]
 
        [use-default-position? (and (= -11111 (list-ref args 2))
-                                   (= -11111 (list-ref args (if dlg? 3 1))))]
+                                   (= -11111 (list-ref args 1)))]
        
        [enabled? #t]
        [focus #f]