diff --git a/packages/starlight/__bench_fn__/generate-route-data.bench.ts b/packages/starlight/__bench_fn__/generate-route-data.bench.ts
index bf487549a..c4b67bc22 100644
--- a/packages/starlight/__bench_fn__/generate-route-data.bench.ts
+++ b/packages/starlight/__bench_fn__/generate-route-data.bench.ts
@@ -1,8 +1,10 @@
+import { klona } from 'klona';
 import { bench, describe, vi } from 'vitest';
 import { getRouteDataTestContext } from '../__tests__/test-utils';
 import { generateRouteData } from '../src/utils/routing/data';
 import { getRouteBySlugParam } from '../src/utils/routing';
-import { getSidebar } from '../src/utils/navigation';
+import { flattenSidebar, getSidebar } from '../src/utils/navigation';
+import type { SidebarEntry } from '../src/utils/routing/types';
 
 const docs = vi.hoisted(() => {
 	const docs: [string, { title: string }][] = [];
@@ -48,3 +50,17 @@ describe('routing', () => {
 		getSidebar(context.url.pathname, route.locale);
 	});
 });
+
+/** Recursive function that simulates the heavier logic in `<SidebarSublist>` rendering. */
+function mockSidebarRender(sublist: SidebarEntry[]) {
+	for (const entry of sublist) {
+		if (entry.type !== 'link') {
+			flattenSidebar(entry.entries).some((i) => i.isCurrent);
+			mockSidebarRender(entry.entries);
+		}
+	}
+}
+
+bench('sidebar current groups', () => {
+	mockSidebarRender(klona(getSidebar(context.url.pathname, route.locale)));
+});