diff --git a/src/server/services/tokenRouter.test.ts b/src/server/services/tokenRouter.test.ts
index e33ecbd..0c92742 100644
--- a/src/server/services/tokenRouter.test.ts
+++ b/src/server/services/tokenRouter.test.ts
@@ -76,6 +76,29 @@ describe('filterRecentlyFailedCandidates', () => {
     expect(result.map((c) => c.id).sort()).toEqual(['a', 'b']);
   });
 
+  it('keeps candidates unchanged when avoidSec is omitted', () => {
+    const nowMs = Date.now();
+    const candidates: Candidate[] = [
+      {
+        id: 'recent-failure',
+        channel: {
+          failCount: 3,
+          lastFailAt: new Date(nowMs - 5 * 1000).toISOString(),
+        },
+      },
+      {
+        id: 'healthy',
+        channel: {
+          failCount: 0,
+          lastFailAt: null,
+        },
+      },
+    ];
+
+    const result = filterRecentlyFailedCandidates(candidates, nowMs);
+    expect(result).toEqual(candidates);
+  });
+
   it('does not penalize stale failures outside the avoidance window', () => {
     const nowMs = Date.now();
     const candidates: Candidate[] = [
diff --git a/src/server/services/tokenRouter.ts b/src/server/services/tokenRouter.ts
index 358a42d..4919e1d 100644
--- a/src/server/services/tokenRouter.ts
+++ b/src/server/services/tokenRouter.ts
@@ -167,13 +167,13 @@ export function filterRecentlyFailedCandidates<T extends { channel: FailureAware
   nowMs = Date.now(),
   avoidSec?: number,
 ): T[] {
-  if (candidates.length <= 1) return candidates;
-  if (avoidSec <= 0) return candidates;
-
+  if (candidates.length <= 1) return candidates;
+  if (avoidSec == null || avoidSec <= 0) return candidates;
+
   const healthy = candidates.filter((candidate) => !isChannelRecentlyFailed(candidate.channel, nowMs, avoidSec));
-  // If all channels failed recently, keep them all and let weight/random decide.
-  return healthy.length > 0 ? healthy : candidates;
-}
+  // If all channels failed recently, keep them all and let weight/random decide.
+  return healthy.length > 0 ? healthy : candidates;
+}
 
 export interface RouteDecisionCandidate {
   channelId: number;