diff --git a/collects/mred/private/wx/cocoa/radio-box.rkt b/collects/mred/private/wx/cocoa/radio-box.rkt
index 237ec581..558418df 100644
--- a/collects/mred/private/wx/cocoa/radio-box.rkt
+++ b/collects/mred/private/wx/cocoa/radio-box.rkt
@@ -26,6 +26,9 @@
   #:mixins (FocusResponder KeyMouseResponder CursorDisplayer)
   [wxb]
   (-a _void (clicked: [_id sender])
+      ;; In case we were in 0-item mode, switch to Radio mode to
+      ;; ensure that only one button is selected:
+      (tellv self setMode: #:type _int NSRadioModeMatrix)
       (queue-window*-event wxb (lambda (wx) (send wx clicked)))))
 
 (define-objc-class MyImageButtonCell NSButtonCell
@@ -127,15 +130,21 @@
     (if (= i -1)
         (begin
           ;; Need to change to NSListModeMatrix to disable all.
-          ;; It seem that we don't have to change the mode back, for some reason.
           (tellv (get-cocoa) setMode: #:type _int NSListModeMatrix)
           (tellv (get-cocoa) deselectAllCells))
-        (tellv (get-cocoa) selectCellAtRow: #:type _NSInteger (if horiz? 0 i)
-               column: #:type _NSInteger (if horiz? i 0))))
+        (begin
+          (tellv (get-cocoa) setMode: #:type _int NSRadioModeMatrix)
+          (tellv (get-cocoa) selectCellAtRow: #:type _NSInteger (if horiz? 0 i)
+                 column: #:type _NSInteger (if horiz? i 0)))))
   (define/public (get-selection)
-    (if horiz?
-        (tell #:type _NSInteger (get-cocoa) selectedColumn)
-        (tell #:type _NSInteger (get-cocoa) selectedRow)))
+    (let ([c (tell (get-cocoa) selectedCell)]
+          [pos (if horiz?
+                   (tell #:type _NSInteger (get-cocoa) selectedColumn)
+                   (tell #:type _NSInteger (get-cocoa) selectedRow))])
+      (if (and c
+               (positive? (tell #:type _NSInteger c state)))
+          pos
+          -1)))
   (define/public (number) count)
 
   (define/override (maybe-register-as-child parent on?)