diff --git a/extensions/acpx/src/runtime.test.ts b/extensions/acpx/src/runtime.test.ts
index ec5e37d9429..6374610f02f 100644
--- a/extensions/acpx/src/runtime.test.ts
+++ b/extensions/acpx/src/runtime.test.ts
@@ -143,8 +143,8 @@ describe("AcpxRuntime fresh reset wrapper", () => {
   });
 
   it("exposes assertSupportedRuntimeSessionMode as a typed guard", () => {
-    expect(() => __testing.assertSupportedRuntimeSessionMode("persistent")).not.toThrow();
-    expect(() => __testing.assertSupportedRuntimeSessionMode("oneshot")).not.toThrow();
+    expect(__testing.assertSupportedRuntimeSessionMode("persistent")).toBeUndefined();
+    expect(__testing.assertSupportedRuntimeSessionMode("oneshot")).toBeUndefined();
     expect(() => __testing.assertSupportedRuntimeSessionMode("run" as never)).toThrow(
       AcpRuntimeError,
     );