diff --git a/ui/src/components/door_map/RectangleCanvas.vue b/ui/src/components/door_map/RectangleCanvas.vue
index 74e638d..90305c0 100644
--- a/ui/src/components/door_map/RectangleCanvas.vue
+++ b/ui/src/components/door_map/RectangleCanvas.vue
@@ -45,7 +45,7 @@ export default class extends Vue {
   private preview_rect = new Rectangle();
   private drag_rect?: Rectangle;
   private drag_origin = new Vector2D();
-  private rectangles: Rectangle[] = [];
+  private rectangles!: Rectangle[];
 
   private get preview_visible(): boolean {
     return this.state !== CanvasState.Idle;