diff --git a/tests/ws-upstream.test.ts b/tests/ws-upstream.test.ts
index b58472eab..bb8f0061b 100644
--- a/tests/ws-upstream.test.ts
+++ b/tests/ws-upstream.test.ts
@@ -1,4 +1,4 @@
-import { afterEach, describe, expect, jest, test } from "bun:test";
+import { afterEach, describe, expect, spyOn, test } from "bun:test";
 import { providerFetch } from "../src/server/responses/fetch-helpers";
 import { codexWsUpstreamFetch, shouldUseCodexWsUpstream } from "../src/server/responses/ws-upstream";
 import type { OcxProviderConfig } from "../src/types";
@@ -190,7 +190,12 @@ describe("codexWsUpstreamFetch", () => {
   });
 
   test("falls back to the HTTP fetch when the upgrade deadline elapses without open or close", async () => {
-    jest.useFakeTimers();
+    let deadline: (() => void) | undefined;
+    const setTimeoutSpy = spyOn(globalThis, "setTimeout").mockImplementation(((callback: () => void, delay?: number) => {
+      expect(delay).toBe(10_000);
+      deadline = callback;
+      return 0;
+    }) as typeof setTimeout);
     try {
       installFake(() => { /* handshake never settles */ });
       const sentinel = new Response("sse-timeout-fallback", { status: 200 });
@@ -202,14 +207,14 @@ describe("codexWsUpstreamFetch", () => {
 
       const responsePromise = codexWsUpstreamFetch(CODEX_URL, streamingInit(), fallback);
       expect(FakeWebSocket.instances).toHaveLength(1);
-      jest.advanceTimersByTime(10_000);
+      deadline?.();
       const response = await responsePromise;
 
       expect(response).toBe(sentinel);
       expect(fallbackCalls).toBe(1);
       expect(FakeWebSocket.instances[0].closed).toBe(true);
     } finally {
-      jest.useRealTimers();
+      setTimeoutSpy.mockRestore();
     }
   });