diff -up widelands-build16-src/src/ui_basic/window.cc~ widelands-build16-src/src/ui_basic/window.cc
--- widelands-build16-src/src/ui_basic/window.cc~	2011-04-15 20:40:26.000000000 +0200
+++ widelands-build16-src/src/ui_basic/window.cc	2011-07-16 15:35:18.976363248 +0200
@@ -250,12 +250,15 @@ void Window::move_inside_parent() {
 */
 void Window::center_to_parent()
 {
-	Panel & parent = *get_parent();
+	Panel *parent = get_parent();
+
+	if (!parent)
+		return;
 
 	set_pos
 		(Point
-		 	((parent.get_inner_w() - get_w()) / 2,
-		 	 (parent.get_inner_h() - get_h()) / 2));
+		 	((parent->get_inner_w() - get_w()) / 2,
+		 	 (parent->get_inner_h() - get_h()) / 2));
 }