diff --git a/packages/backend/migration/1659446758000-fix-thread-id.js b/packages/backend/migration/1659446758000-fix-thread-id.js
new file mode 100644
index 000000000..edd5712a2
--- /dev/null
+++ b/packages/backend/migration/1659446758000-fix-thread-id.js
@@ -0,0 +1,30 @@
+export class fixThreadId1659446758000 {
+	name = 'fixThreadId1659446758000'
+
+	async up(queryRunner) {
+		await Promise.all([
+			queryRunner.query(`UPDATE "note" SET "threadId" = "id" WHERE "replyId" IS NULL`),
+			queryRunner.query(`WITH "threads" ("noteId", "thread") AS (
+			    SELECT "id" as "noteId", "parent" as "thread" FROM (
+			        WITH RECURSIVE "parents" ("id", "parent", "height") AS (
+			                SELECT "id", "replyId", 0 FROM "note" WHERE "replyId" IS NOT NULL AND "threadId" IS NULL
+			            UNION ALL
+			                SELECT "parents"."id", "note"."replyId", "parents"."height" + 1
+			                FROM "parents"
+			                JOIN "note" ON "parents"."parent" = "note"."id"
+			                WHERE "note"."replyId" IS NOT NULL
+			        ) SELECT *, MAX("height") OVER (PARTITION BY "id") AS "maxheight" FROM "parents"
+			    ) AS "x"
+			    WHERE "height" = "maxheight"
+			) UPDATE "note" SET "threadId" = "threads"."thread" FROM "threads" WHERE "id" = "threads"."noteId"`),
+		]);
+		await queryRunner.query(`ALTER TABLE "note" ALTER COLUMN "threadId" SET NOT NULL`);
+	}
+
+	async down(queryRunner) {
+		await queryRunner.query(`ALTER TABLE "note" ALTER COLUMN "threaadId" DROP NOT NULL`);
+		// Cannot un-fix thread id's for ones that just were not migrated (2nd query above)
+		// but can remove the thread ids for the root notes of each thread.
+		await queryRunner.query(`UPDATE "note" SET "threadId" = NULL WHERE "replyId" IS NULL`);
+	}
+}
diff --git a/packages/backend/src/models/entities/note.ts b/packages/backend/src/models/entities/note.ts
index 0e15921b7..0181ed772 100644
--- a/packages/backend/src/models/entities/note.ts
+++ b/packages/backend/src/models/entities/note.ts
@@ -51,7 +51,7 @@ export class Note {
 	@Column('varchar', {
 		length: 256, nullable: true,
 	})
-	public threadId: string | null;
+	public threadId: string;
 
 	@Column('text', {
 		nullable: true,
diff --git a/packages/backend/src/server/api/common/generate-muted-note-thread-query.ts b/packages/backend/src/server/api/common/generate-muted-note-thread-query.ts
index 681ec4eb2..153893032 100644
--- a/packages/backend/src/server/api/common/generate-muted-note-thread-query.ts
+++ b/packages/backend/src/server/api/common/generate-muted-note-thread-query.ts
@@ -7,11 +7,7 @@ export function generateMutedNoteThreadQuery(q: SelectQueryBuilder<any>, me: { i
 		.select('threadMuted.threadId')
 		.where('threadMuted.userId = :userId', { userId: me.id });
 
-	q.andWhere(`note.id NOT IN (${ mutedQuery.getQuery() })`);
-	q.andWhere(new Brackets(qb => { qb
-		.where('note.threadId IS NULL')
-		.orWhere(`note.threadId NOT IN (${ mutedQuery.getQuery() })`);
-	}));
+	q.andWhere(`note.threadId NOT IN (${ mutedQuery.getQuery() })`);
 
 	q.setParameters(mutedQuery.getParameters());
 }
diff --git a/packages/backend/src/server/api/endpoints/notes/state.ts b/packages/backend/src/server/api/endpoints/notes/state.ts
index 67579b2a6..87b56c349 100644
--- a/packages/backend/src/server/api/endpoints/notes/state.ts
+++ b/packages/backend/src/server/api/endpoints/notes/state.ts
@@ -57,7 +57,7 @@ export default define(meta, paramDef, async (ps, user) => {
 		NoteThreadMutings.count({
 			where: {
 				userId: user.id,
-				threadId: note.threadId || note.id,
+				threadId: note.threadId,
 			},
 			take: 1,
 		}),
diff --git a/packages/backend/src/server/api/endpoints/notes/thread-muting/create.ts b/packages/backend/src/server/api/endpoints/notes/thread-muting/create.ts
index dddb55fcb..9da5f4d90 100644
--- a/packages/backend/src/server/api/endpoints/notes/thread-muting/create.ts
+++ b/packages/backend/src/server/api/endpoints/notes/thread-muting/create.ts
@@ -41,9 +41,7 @@ export default define(meta, paramDef, async (ps, user) => {
 
 	const mutedNotes = await Notes.find({
 		where: [{
-			id: note.threadId || note.id,
-		}, {
-			threadId: note.threadId || note.id,
+			threadId: note.threadId,
 		}],
 	});
 
@@ -52,7 +50,7 @@ export default define(meta, paramDef, async (ps, user) => {
 	await NoteThreadMutings.insert({
 		id: genId(),
 		createdAt: new Date(),
-		threadId: note.threadId || note.id,
+		threadId: note.threadId,
 		userId: user.id,
 		mutingNotificationTypes: ps.mutingNotificationTypes,
 	});
diff --git a/packages/backend/src/server/api/endpoints/notes/thread-muting/delete.ts b/packages/backend/src/server/api/endpoints/notes/thread-muting/delete.ts
index c1ea564eb..1a9b803e7 100644
--- a/packages/backend/src/server/api/endpoints/notes/thread-muting/delete.ts
+++ b/packages/backend/src/server/api/endpoints/notes/thread-muting/delete.ts
@@ -29,7 +29,7 @@ export default define(meta, paramDef, async (ps, user) => {
 	});
 
 	await NoteThreadMutings.delete({
-		threadId: note.threadId || note.id,
+		threadId: note.threadId,
 		userId: user.id,
 	});
 });
diff --git a/packages/backend/src/services/note/create.ts b/packages/backend/src/services/note/create.ts
index 2cae03241..41ef2a053 100644
--- a/packages/backend/src/services/note/create.ts
+++ b/packages/backend/src/services/note/create.ts
@@ -369,7 +369,7 @@ export default async (user: { id: User['id']; username: User['username']; host:
 			if (data.reply.userHost === null) {
 				const threadMuted = await NoteThreadMutings.findOneBy({
 					userId: data.reply.userId,
-					threadId: data.reply.threadId || data.reply.id,
+					threadId: data.reply.threadId,
 				});
 
 				if (!threadMuted) {
@@ -500,15 +500,16 @@ function incRenoteCount(renote: Note): void {
 
 async function insertNote(user: { id: User['id']; host: User['host']; }, data: Option, tags: string[], emojis: string[], mentionedUsers: MinimumUser[]): Promise<Note> {
 	const createdAt = data.createdAt ?? new Date();
+	const id = genId(createdAt);
 
 	const insert = new Note({
-		id: genId(createdAt),
+		id,
 		createdAt,
-		fileIds: data.files?.map(file => file.id) ?? [],
-		replyId: data.reply?.id ?? null,
-		renoteId: data.renote?.id ?? null,
-		channelId: data.channel?.id ?? null,
-		threadId: data.reply?.threadId ?? data.reply?.id ?? null,
+		fileIds: data.files ? data.files.map(file => file.id) : [],
+		replyId: data.reply ? data.reply.id : null,
+		renoteId: data.renote ? data.renote.id : null,
+		channelId: data.channel ? data.channel.id : null,
+		threadId: data.reply?.threadId ?? id,
 		name: data.name,
 		text: data.text,
 		hasPoll: data.poll != null,
@@ -616,7 +617,7 @@ async function createMentionedEvents(mentionedUsers: MinimumUser[], note: Note,
 	for (const u of mentionedUsers.filter(u => Users.isLocalUser(u))) {
 		const threadMuted = await NoteThreadMutings.findOneBy({
 			userId: u.id,
-			threadId: note.threadId || note.id,
+			threadId: note.threadId,
 		});
 
 		if (threadMuted) {
diff --git a/packages/backend/src/services/note/unread.ts b/packages/backend/src/services/note/unread.ts
index 829a024ee..12c83e8a5 100644
--- a/packages/backend/src/services/note/unread.ts
+++ b/packages/backend/src/services/note/unread.ts
@@ -20,7 +20,7 @@ export async function insertNoteUnread(userId: User['id'], note: Note, params: {
 	// スレッドミュート
 	const threadMute = await NoteThreadMutings.findOneBy({
 		userId,
-		threadId: note.threadId || note.id,
+		threadId: note.threadId,
 	});
 	if (threadMute) return;