diff --git a/backend/src/services/db.service.test.ts b/backend/src/services/db.service.test.ts
index fcd4dc6..2052cc9 100644
--- a/backend/src/services/db.service.test.ts
+++ b/backend/src/services/db.service.test.ts
@@ -437,6 +437,7 @@ describe('DbService v2 methods', () => {
       await expect(service.serveNextVibePlanItem('session-1', 'user-1')).resolves.toEqual({ item, stale: false });
       expect(clientQuery.mock.calls[1][0]).toContain('FOR UPDATE');
       expect(clientQuery.mock.calls[3][0]).toContain('SET committed = true');
+      expect(clientQuery.mock.calls[3][1]).toEqual(['plan-1']);
       expect(clientQuery.mock.calls[4][0]).toContain("'track_served'");
     });
 
diff --git a/backend/src/services/db.service.ts b/backend/src/services/db.service.ts
index d0014de..11f66e0 100644
--- a/backend/src/services/db.service.ts
+++ b/backend/src/services/db.service.ts
@@ -2203,12 +2203,12 @@ export class DbService {
       const item = await client.query(
         `WITH next_item AS (
            SELECT i.plan_version_id, i.ordinal FROM vibe_plan_items i
-           WHERE i.plan_version_id = $2 AND NOT i.committed ORDER BY i.ordinal ASC LIMIT 1 FOR UPDATE
+           WHERE i.plan_version_id = $1 AND NOT i.committed ORDER BY i.ordinal ASC LIMIT 1 FOR UPDATE
          )
          UPDATE vibe_plan_items i SET committed = true
          FROM next_item n WHERE i.plan_version_id = n.plan_version_id AND i.ordinal = n.ordinal
          RETURNING i.*`,
-        [sessionId, plan.id]
+        [plan.id]
       );
       const served = item.rows[0] as VibePlanItem | undefined;
       if (!served) return { item: null, stale: false };