diff --git a/packages/das/src/webhook/repo-backfill-schedule.service.ts b/packages/das/src/webhook/repo-backfill-schedule.service.ts
index f7c4c49..8b47dde 100644
--- a/packages/das/src/webhook/repo-backfill-schedule.service.ts
+++ b/packages/das/src/webhook/repo-backfill-schedule.service.ts
@@ -25,10 +25,22 @@ const BACKFILL_TZ = "America/Chicago";
 const BACKFILL_DAYS = Number(
   process.env.NIGHTLY_BACKFILL_DAYS ?? DEFAULT_BACKFILL_DAYS,
 );
+const MIN_BACKFILL_DAYS = 1;
+const MAX_BACKFILL_DAYS = 365;
+
+function parseBackfillDays(rawValue: number): number {
+  if (!Number.isFinite(rawValue)) return DEFAULT_BACKFILL_DAYS;
+  const normalized = Math.floor(rawValue);
+  if (normalized < MIN_BACKFILL_DAYS || normalized > MAX_BACKFILL_DAYS) {
+    return DEFAULT_BACKFILL_DAYS;
+  }
+  return normalized;
+}
 
 @Injectable()
 export class RepoBackfillScheduleService implements OnModuleInit {
   private readonly logger = new Logger(RepoBackfillScheduleService.name);
+  private readonly backfillDays = parseBackfillDays(BACKFILL_DAYS);
 
   constructor(
     @InjectRepository(Repo)
@@ -44,6 +56,12 @@ export class RepoBackfillScheduleService implements OnModuleInit {
       );
       return;
     }
+    if (this.backfillDays !== BACKFILL_DAYS) {
+      this.logger.warn(
+        `Invalid NIGHTLY_BACKFILL_DAYS=${String(process.env.NIGHTLY_BACKFILL_DAYS)}; ` +
+          `using ${this.backfillDays} days`,
+      );
+    }
     this.logger.log(
       `Nightly repo backfill scheduled '${BACKFILL_CRON}' (${BACKFILL_TZ})`,
     );
@@ -62,13 +80,13 @@ export class RepoBackfillScheduleService implements OnModuleInit {
 
       this.logger.log(
         `Enqueuing nightly backfill for ${repos.length} repos ` +
-          `(last ${BACKFILL_DAYS}d)`,
+          `(last ${this.backfillDays}d)`,
       );
 
       for (const repo of repos) {
         await this.fetchQueue.add(
           FETCH_JOBS.BACKFILL_REPO,
-          { repoFullName: repo.repoFullName, days: BACKFILL_DAYS },
+          { repoFullName: repo.repoFullName, days: this.backfillDays },
           {
             // Static per-repo jobId so a still-running nightly backfill isn't
             // stacked on by the next tick. Distinct from the admin endpoint's