diff --git a/CHANGELOG.md b/CHANGELOG.md
index a53d506ef5867ef81b48f02177412da4d739b305..5b2b4784afea95b9e741fe96adc4ddb0746507ed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -44,6 +44,7 @@
 - bullをbull-mqにアップグレードし、ジョブキューのパフォーマンスを改善
 - ストリーミングのパフォーマンスを改善
 - Fix: お知らせの画像URLを空にできない問題を修正
+- Fix: i/notificationsのsinceIdが機能しない問題を修正
 
 ## 13.12.2
 
diff --git a/packages/backend/src/server/api/endpoints/i/notifications.ts b/packages/backend/src/server/api/endpoints/i/notifications.ts
index e141be764a795b483f00dd4f50a00a39f83c2b8d..f5662f4a0e819f876ca8620d9b84a45bbe32b3a2 100644
--- a/packages/backend/src/server/api/endpoints/i/notifications.ts
+++ b/packages/backend/src/server/api/endpoints/i/notifications.ts
@@ -91,18 +91,18 @@ export default class extends Endpoint<typeof meta, typeof paramDef> {
 			const includeTypes = ps.includeTypes && ps.includeTypes.filter(type => !(obsoleteNotificationTypes).includes(type as any)) as typeof notificationTypes[number][];
 			const excludeTypes = ps.excludeTypes && ps.excludeTypes.filter(type => !(obsoleteNotificationTypes).includes(type as any)) as typeof notificationTypes[number][];
 
-			const limit = ps.limit + (ps.untilId ? 1 : 0); // untilIdに指定したものも含まれるため+1
+			const limit = ps.limit + (ps.untilId ? 1 : 0) + (ps.sinceId ? 1 : 0); // untilIdに指定したものも含まれるため+1
 			const notificationsRes = await this.redisClient.xrevrange(
 				`notificationTimeline:${me.id}`,
 				ps.untilId ? this.idService.parse(ps.untilId).date.getTime() : '+',
-				'-',
+				ps.sinceId ? this.idService.parse(ps.sinceId).date.getTime() : '-',
 				'COUNT', limit);
 
 			if (notificationsRes.length === 0) {
 				return [];
 			}
 
-			let notifications = notificationsRes.map(x => JSON.parse(x[1][1])).filter(x => x.id !== ps.untilId) as Notification[];
+			let notifications = notificationsRes.map(x => JSON.parse(x[1][1])).filter(x => x.id !== ps.untilId && x !== ps.sinceId) as Notification[];
 
 			if (includeTypes && includeTypes.length > 0) {
 				notifications = notifications.filter(notification => includeTypes.includes(notification.type));