diff --git a/src/lib/__tests__/cardLayout.test.ts b/src/lib/__tests__/cardLayout.test.ts
index 2342648..81f1fa8 100644
--- a/src/lib/__tests__/cardLayout.test.ts
+++ b/src/lib/__tests__/cardLayout.test.ts
@@ -49,6 +49,22 @@ describe("cardLayout utilities", () => {
   });
 
 describe("toggleBlockVisibility", () => {
+
+    it("toggles block visibility correctly for a custom mock layout and preserves extra properties", () => {
+      const mockLayout = {
+        extraProp: "preserved",
+        blocks: [
+          { id: "profile" as const, visible: true, column: "full" as const },
+          { id: "stats" as const, visible: false, column: "left" as const }
+        ]
+      } as unknown as import("../types").CardLayout;
+
+      const next = toggleBlockVisibility(mockLayout, "profile");
+
+      expect(next).toHaveProperty("extraProp", "preserved");
+      expect(next.blocks.find(b => b.id === "profile")?.visible).toBe(false);
+      expect(next.blocks.find(b => b.id === "stats")?.visible).toBe(false);
+    });
     it("toggles block visibility to false", () => {
       const layout = cloneDefaultCardLayout(); // 'bio' is visible by default
       const next = toggleBlockVisibility(layout, "bio");
diff --git a/src/lib/cardLayout.ts b/src/lib/cardLayout.ts
index 16f4f38..f30a493 100644
--- a/src/lib/cardLayout.ts
+++ b/src/lib/cardLayout.ts
@@ -70,6 +70,7 @@ export function normalizeCardLayout(input: unknown): CardLayout {
 
 export function toggleBlockVisibility(layout: CardLayout, blockId: CardBlockId): CardLayout {
     return {
+        ...layout,
         blocks: layout.blocks.map((block) =>
             block.id === blockId ? { ...block, visible: !block.visible } : block
         ),