diff -r 5dc02b23752f -r 3e2da88830cd src/gui/kernel/qcocoasharedwindowmethods_mac_p.h
--- a/src/gui/kernel/qcocoasharedwindowmethods_mac_p.h	Tue Jul 06 15:10:48 2010 +0300
+++ b/src/gui/kernel/qcocoasharedwindowmethods_mac_p.h	Wed Aug 18 10:37:55 2010 +0300
@@ -85,6 +85,8 @@
 - (BOOL)canBecomeKeyWindow
 {
     QWidget *widget = [self QT_MANGLE_NAMESPACE(qt_qwidget)];
+    if (!widget)
+        return NO; // This should happen only for qt_root_win
 
     bool isToolTip = (widget->windowType() == Qt::ToolTip);
     bool isPopup = (widget->windowType() == Qt::Popup);
@@ -94,6 +96,8 @@
 - (BOOL)canBecomeMainWindow
 {
     QWidget *widget = [self QT_MANGLE_NAMESPACE(qt_qwidget)];
+    if (!widget)
+        return NO; // This should happen only for qt_root_win
 
     bool isToolTip = (widget->windowType() == Qt::ToolTip);
     bool isPopup = (widget->windowType() == Qt::Popup);