diff --git a/src/msw/radiobox.cpp b/src/msw/radiobox.cpp
index c8f410dc26..af016c9a15 100644
--- a/src/msw/radiobox.cpp
+++ b/src/msw/radiobox.cpp
@@ -206,6 +206,10 @@ bool wxRadioBox::Create(wxWindow *parent,
     SetWindowPos(GetHwnd(), HWND_BOTTOM, 0, 0, 0, 0, SWP_NOMOVE|SWP_NOSIZE);
 #endif
 
+    // Have to invalidate the best size as it may have been calculated
+    // before the number of buttons was known
+    InvalidateBestSize();
+
     SetMajorDim(majorDim == 0 ? n : majorDim, style);
     SetSelection(0);
     SetSize(pos.x, pos.y, size.x, size.y);