diff --git a/src/test/harness.ts b/src/test/harness.ts
index 245ed78..d635e67 100644
--- a/src/test/harness.ts
+++ b/src/test/harness.ts
@@ -518,7 +518,7 @@ export function createTestHarness(): TestHarness {
     },
 
     // Timer helper - requires vi.useFakeTimers() to be active
-    advanceTimers: () => vi.runAllTimersAsync(),
+    advanceTimers: async () => { await vi.runAllTimersAsync(); },
 
     withFakeTimers: async (fn: () => Promise<void>) => {
       vi.useFakeTimers();