diff --git a/src/bridge_gui.cpp b/src/bridge_gui.cpp
--- a/src/bridge_gui.cpp
+++ b/src/bridge_gui.cpp
@@ -329,6 +329,7 @@ static const NWidgetPart _nested_build_b
 	NWidget(NWID_HORIZONTAL),
 		NWidget(WWT_CLOSEBOX, COLOUR_DARK_GREEN),
 		NWidget(WWT_CAPTION, COLOUR_DARK_GREEN, WID_BBS_CAPTION), SetDataTip(STR_SELECT_RAIL_BRIDGE_CAPTION, STR_TOOLTIP_WINDOW_TITLE_DRAG_THIS),
+		NWidget(WWT_DEFSIZEBOX, COLOUR_DARK_GREEN),
 	EndContainer(),
 
 	NWidget(NWID_HORIZONTAL),