diff --git a/app/usage.test.js b/app/usage.test.js
index 21655fc..783c9c7 100644
--- a/app/usage.test.js
+++ b/app/usage.test.js
@@ -210,6 +210,13 @@ describe('resolveRemainingPercent', () => {
     }
   });
 
+  it('returns null percent when rate.remaining is null/undefined', () => {
+    for (const remaining of [null, undefined]) {
+      const pct = resolveRemainingPercent({ available: false, reason: 'x' }, { hasData: true, remaining, limit: 200000, kind: 'tokens' });
+      assert.equal(pct.percent, null, `rate.remaining=${remaining} 應算不出百分比`);
+    }
+  });
+
   it('returns null percent when limit is finite but remaining is non-finite', () => {
     const pct = resolveRemainingPercent({ available: true, used: 0, limit: 100, remaining: Infinity, currency: 'USD' }, null);
     assert.equal(pct.percent, null);