diff --git a/src/misc_gui.cpp b/src/misc_gui.cpp
--- a/src/misc_gui.cpp
+++ b/src/misc_gui.cpp
@@ -593,9 +593,9 @@ public:
 		 * Add a fixed distance 20 to make it less cluttered.
 		 */
 		const Window *w = FindWindowById(WC_MAIN_TOOLBAR, 0);
-		int scr_top = w->top + w->height + 20;
+		int scr_top = ((w != NULL) ? w->top + w->height : 0) + 20;
 		w = FindWindowById(WC_STATUS_BAR, 0);
-		int scr_bot = w->top - 20;
+		int scr_bot = ((w != NULL) ? w->top : _screen.height) - 20;
 
 		Point pt = RemapCoords2(this->position.x, this->position.y);
 		const ViewPort *vp = FindWindowById(WC_MAIN_WINDOW, 0)->viewport;
@@ -810,9 +810,9 @@ struct TooltipsWindow : public Window
 		 * Add a fixed distance 2 so the tooltip floats free from both bars.
 		 */
 		const Window *w = FindWindowById(WC_MAIN_TOOLBAR, 0);
-		int scr_top = w->top + w->height + 2;
+		int scr_top = ((w != NULL) ? w->top + w->height : 0) + 2;
 		w = FindWindowById(WC_STATUS_BAR, 0);
-		int scr_bot = w->top - 2;
+		int scr_bot = ((w != NULL) ? w->top : _screen.height) - 2;
 
 		Point pt;