diff --git a/invokeai/frontend/web/src/features/controlLayers/konva/util.test.ts b/invokeai/frontend/web/src/features/controlLayers/konva/util.test.ts
new file mode 100644
index 0000000000..a7db030ae4
--- /dev/null
+++ b/invokeai/frontend/web/src/features/controlLayers/konva/util.test.ts
@@ -0,0 +1,47 @@
+import { getPrefixedId, getRectUnion } from 'features/controlLayers/konva/util';
+import { describe, expect, it } from 'vitest';
+
+describe('util', () => {
+  describe('getPrefixedId', () => {
+    it('should return a prefixed id', () => {
+      expect(getPrefixedId('foo').split(':')[0]).toBe('foo');
+    });
+  });
+
+  describe('getRectUnion', () => {
+    it('should return the union of rects (2 rects)', () => {
+      const rect1 = { x: 0, y: 0, width: 10, height: 10 };
+      const rect2 = { x: 5, y: 5, width: 10, height: 10 };
+      const union = getRectUnion(rect1, rect2);
+      expect(union).toEqual({ x: 0, y: 0, width: 15, height: 15 });
+    });
+    it('should return the union of rects (3 rects)', () => {
+      const rect1 = { x: 0, y: 0, width: 10, height: 10 };
+      const rect2 = { x: 5, y: 5, width: 10, height: 10 };
+      const rect3 = { x: 10, y: 10, width: 10, height: 10 };
+      const union = getRectUnion(rect1, rect2, rect3);
+      expect(union).toEqual({ x: 0, y: 0, width: 20, height: 20 });
+    });
+    it('should return the union of rects (2 rects none from zero)', () => {
+      const rect1 = { x: 5, y: 5, width: 10, height: 10 };
+      const rect2 = { x: 10, y: 10, width: 10, height: 10 };
+      const union = getRectUnion(rect1, rect2);
+      expect(union).toEqual({ x: 5, y: 5, width: 15, height: 15 });
+    });
+    it('should return the union of rects (2 rects with negative x/y)', () => {
+      const rect1 = { x: -5, y: -5, width: 10, height: 10 };
+      const rect2 = { x: 0, y: 0, width: 10, height: 10 };
+      const union = getRectUnion(rect1, rect2);
+      expect(union).toEqual({ x: -5, y: -5, width: 15, height: 15 });
+    });
+    it('should return the union of the first rect if only one rect is provided', () => {
+      const rect = { x: 0, y: 0, width: 10, height: 10 };
+      const union = getRectUnion(rect);
+      expect(union).toEqual(rect);
+    });
+    it('should fall back on an empty rect if no rects are provided', () => {
+      const union = getRectUnion();
+      expect(union).toEqual({ x: 0, y: 0, width: 0, height: 0 });
+    });
+  });
+});
diff --git a/invokeai/frontend/web/src/features/controlLayers/konva/util.ts b/invokeai/frontend/web/src/features/controlLayers/konva/util.ts
index eea14e02ba..c6e42aca27 100644
--- a/invokeai/frontend/web/src/features/controlLayers/konva/util.ts
+++ b/invokeai/frontend/web/src/features/controlLayers/konva/util.ts
@@ -418,19 +418,25 @@ export function snapToNearest(value: number, candidateValues: number[], threshol
 }
 
 /**
- * Gets the union of two rects
- * @param rect1 The first rect
- * @param rect2 The second rect
+ * Gets the union of any number of rects.
+ * @params rects The rects to union
  * @returns The union of the two rects
  */
 export const getRectUnion = (...rects: Rect[]): Rect => {
+  const firstRect = rects.shift();
+
+  if (!firstRect) {
+    return getEmptyRect();
+  }
+
   const rect = rects.reduce<Rect>((acc, r) => {
     const x = Math.min(acc.x, r.x);
     const y = Math.min(acc.y, r.y);
     const width = Math.max(acc.x + acc.width, r.x + r.width) - x;
     const height = Math.max(acc.y + acc.height, r.y + r.height) - y;
     return { x, y, width, height };
-  }, getEmptyRect());
+  }, firstRect);
+
   return rect;
 };