diff --git a/src/ai/ai_gui.cpp b/src/ai/ai_gui.cpp
--- a/src/ai/ai_gui.cpp
+++ b/src/ai/ai_gui.cpp
@@ -240,6 +240,7 @@ static const NWidgetPart _nested_ai_list
 	NWidget(NWID_HORIZONTAL),
 		NWidget(WWT_CLOSEBOX, COLOUR_MAUVE),
 		NWidget(WWT_CAPTION, COLOUR_MAUVE, WID_AIL_CAPTION), SetDataTip(STR_AI_LIST_CAPTION, STR_TOOLTIP_WINDOW_TITLE_DRAG_THIS),
+		NWidget(WWT_DEFSIZEBOX, COLOUR_MAUVE),
 	EndContainer(),
 	NWidget(NWID_HORIZONTAL),
 		NWidget(WWT_MATRIX, COLOUR_MAUVE, WID_AIL_LIST), SetMinimalSize(188, 112), SetFill(1, 1), SetResize(1, 1), SetDataTip(0x501, STR_AI_LIST_TOOLTIP), SetScrollbar(WID_AIL_SCROLLBAR),
@@ -588,6 +589,7 @@ static const NWidgetPart _nested_ai_sett
 	NWidget(NWID_HORIZONTAL),
 		NWidget(WWT_CLOSEBOX, COLOUR_MAUVE),
 		NWidget(WWT_CAPTION, COLOUR_MAUVE, WID_AIS_CAPTION), SetDataTip(STR_AI_SETTINGS_CAPTION, STR_TOOLTIP_WINDOW_TITLE_DRAG_THIS),
+		NWidget(WWT_DEFSIZEBOX, COLOUR_MAUVE),
 	EndContainer(),
 	NWidget(NWID_HORIZONTAL),
 		NWidget(WWT_MATRIX, COLOUR_MAUVE, WID_AIS_BACKGROUND), SetMinimalSize(188, 182), SetResize(1, 1), SetFill(1, 0), SetDataTip(0x501, STR_NULL), SetScrollbar(WID_AIS_SCROLLBAR),
@@ -1447,6 +1449,7 @@ static const NWidgetPart _nested_ai_debu
 		NWidget(WWT_CLOSEBOX, COLOUR_GREY),
 		NWidget(WWT_CAPTION, COLOUR_GREY), SetDataTip(STR_AI_DEBUG, STR_TOOLTIP_WINDOW_TITLE_DRAG_THIS),
 		NWidget(WWT_SHADEBOX, COLOUR_GREY),
+		NWidget(WWT_DEFSIZEBOX, COLOUR_GREY),
 		NWidget(WWT_STICKYBOX, COLOUR_GREY),
 	EndContainer(),
 	NWidget(WWT_PANEL, COLOUR_GREY, WID_AID_VIEW),