diff --git a/src/bounties/bounties.service.spec.ts b/src/bounties/bounties.service.spec.ts
index 405e3d2..81231a3 100644
--- a/src/bounties/bounties.service.spec.ts
+++ b/src/bounties/bounties.service.spec.ts
@@ -259,24 +259,47 @@ describe('BountiesService', () => {
     expect(bounty.status).toBe(BountyStatus.REFUNDED);
   });
 
-  it('expireOverdue flips overdue bounties to EXPIRED and returns count', async () => {
-    const overdueBounties = [
-      { id: 'b1', status: BountyStatus.OPEN },
-      { id: 'b2', status: BountyStatus.FUNDED },
-    ];
-    const mockQueryBuilder = {
+  it('expireOverdue atomically flips overdue bounties to EXPIRED via a conditional update and returns affected count', async () => {
+    const qb = {
+      update: jest.fn().mockReturnThis(),
+      set: jest.fn().mockReturnThis(),
       where: jest.fn().mockReturnThis(),
       andWhere: jest.fn().mockReturnThis(),
-      getMany: jest.fn().mockResolvedValue(overdueBounties),
+      execute: jest.fn().mockResolvedValue({ affected: 2 }),
     };
-    bountyRepo.createQueryBuilder.mockReturnValue(mockQueryBuilder);
+    bountyRepo.createQueryBuilder.mockReturnValue(qb);
 
     const count = await service.expireOverdue();
 
     expect(count).toBe(2);
-    expect(bountyRepo.save).toHaveBeenCalledTimes(2);
-    expect(overdueBounties[0].status).toBe(BountyStatus.EXPIRED);
-    expect(overdueBounties[1].status).toBe(BountyStatus.EXPIRED);
+    expect(qb.set).toHaveBeenCalledWith({ status: BountyStatus.EXPIRED });
+    expect(qb.andWhere).toHaveBeenCalledWith(
+      'status IN (:...statuses)',
+      { statuses: [BountyStatus.OPEN, BountyStatus.FUNDED, BountyStatus.CLAIMED] },
+    );
+    expect(bountyRepo.save).not.toHaveBeenCalled();
+  });
+
+  it('expireOverdue does not expire a bounty whose status advanced after it was read', async () => {
+    // Simulates a concurrent webhook moving CLAIMED -> IN_REVIEW between the
+    // scan and the write: the conditional UPDATE matches zero rows.
+    const qb = {
+      update: jest.fn().mockReturnThis(),
+      set: jest.fn().mockReturnThis(),
+      where: jest.fn().mockReturnThis(),
+      andWhere: jest.fn().mockReturnThis(),
+      execute: jest.fn().mockResolvedValue({ affected: 0 }),
+    };
+    bountyRepo.createQueryBuilder.mockReturnValue(qb);
+
+    const count = await service.expireOverdue();
+
+    expect(count).toBe(0);
+    expect(qb.andWhere).toHaveBeenCalledWith(
+      'status IN (:...statuses)',
+      { statuses: [BountyStatus.OPEN, BountyStatus.FUNDED, BountyStatus.CLAIMED] },
+    );
+    expect(bountyRepo.save).not.toHaveBeenCalled();
   });
 
   it('markPrClosedWithoutMerge transitions IN_REVIEW back to CLAIMED', async () => {
diff --git a/src/bounties/bounties.service.ts b/src/bounties/bounties.service.ts
index b1a0f8a..12603a4 100644
--- a/src/bounties/bounties.service.ts
+++ b/src/bounties/bounties.service.ts
@@ -274,27 +274,26 @@ export class BountiesService {
     return this.bountyRepo.save(bounty);
   }
 
-  /** Marks bounties whose deadline has passed and that were never merged as expired. */
+  /**
+   * Marks bounties whose deadline has passed and that were never merged as
+   * expired. The status filter and the write are a single conditional UPDATE,
+   * so a bounty advanced concurrently (e.g. CLAIMED -> IN_REVIEW/MERGED/PAID)
+   * is never overwritten with a stale status.
+   */
   async expireOverdue(): Promise<number> {
-    const overdue = await this.bountyRepo
-      .createQueryBuilder('bounty')
-      .where('bounty.deadline IS NOT NULL AND bounty.deadline < :now', {
-        now: new Date(),
-      })
-      .andWhere('bounty.status IN (:...statuses)', {
-        statuses: [
-          BountyStatus.OPEN,
-          BountyStatus.FUNDED,
-          BountyStatus.CLAIMED,
-        ],
-      })
-      .getMany();
-
-    for (const bounty of overdue) {
-      bounty.status = BountyStatus.EXPIRED;
-      await this.bountyRepo.save(bounty);
-    }
-    return overdue.length;
+    const expirable: BountyStatus[] = [
+      BountyStatus.OPEN,
+      BountyStatus.FUNDED,
+      BountyStatus.CLAIMED,
+    ];
+    const result = await this.bountyRepo
+      .createQueryBuilder()
+      .update(Bounty)
+      .set({ status: BountyStatus.EXPIRED })
+      .where('deadline IS NOT NULL AND deadline < :now', { now: new Date() })
+      .andWhere('status IN (:...statuses)', { statuses: expirable })
+      .execute();
+    return result.affected ?? 0;
   }
 
   async list(options: ListBountiesOptions = {}): Promise<Bounty[]> {
diff --git a/src/bounties/bounty-expiry.scheduler.ts b/src/bounties/bounty-expiry.scheduler.ts
index 58b79c9..6f3c0a5 100644
--- a/src/bounties/bounty-expiry.scheduler.ts
+++ b/src/bounties/bounty-expiry.scheduler.ts
@@ -14,6 +14,11 @@ import { BountiesService } from './bounties.service';
  * This is deliberately independent of (and runs prior to) any on-chain
  * auto-refund follow-up for expired FUNDED bounties (#26): the local status
  * flip has to happen regardless.
+ *
+ * Concurrency note: `expireOverdue()` performs a single conditional UPDATE
+ * that only touches rows still in OPEN/FUNDED/CLAIMED at write time, so a
+ * bounty advanced concurrently by a webhook (e.g. CLAIMED -> IN_REVIEW ->
+ * MERGED/PAID) is never clobbered back to EXPIRED.
  */
 @Injectable()
 export class BountyExpiryScheduler {