diff --git a/src/group_gui.cpp b/src/group_gui.cpp
--- a/src/group_gui.cpp
+++ b/src/group_gui.cpp
@@ -37,6 +37,7 @@ static const NWidgetPart _nested_group_w
 		NWidget(WWT_CLOSEBOX, COLOUR_GREY),
 		NWidget(WWT_CAPTION, COLOUR_GREY, WID_GL_CAPTION),
 		NWidget(WWT_SHADEBOX, COLOUR_GREY),
+		NWidget(WWT_DEFSIZEBOX, COLOUR_GREY),
 		NWidget(WWT_STICKYBOX, COLOUR_GREY),
 	EndContainer(),
 	NWidget(NWID_HORIZONTAL),