diff -r 3aa07f06a4b7 -r 31d52bbe209c windowing/windowserver/nga/SERVER/REDRAWQ.CPP
--- a/windowing/windowserver/nga/SERVER/REDRAWQ.CPP	Tue Apr 20 16:38:10 2010 +0100
+++ b/windowing/windowserver/nga/SERVER/REDRAWQ.CPP	Fri Apr 23 14:57:14 2010 +0100
@@ -170,7 +170,9 @@
 	TInt invalidWindows = 0;
 	for (TInt screenNo = 0; screenNo < CWsTop::NumberOfScreens(); ++screenNo)
 		{
-		CWsRootWindow* rootWindow = CWsTop::Screen(screenNo)->RootWindow();
+		const CScreen* screen = CWsTop::Screen(screenNo);
+		WS_ASSERT_ALWAYS(screen, EWsPanicNoScreen);
+		CWsRootWindow* rootWindow = screen->RootWindow();
 		for (CWsWindowGroup *groupWin = rootWindow->Child(); groupWin; groupWin = groupWin->NextSibling())
 			{
 			if (groupWin->WsOwner() == iWsOwner)