diff --git a/packages/backend/migration/1750729939704-FixAvatarUrl.js b/packages/backend/migration/1750729939704-FixAvatarUrl.js
new file mode 100644
index 0000000000..81a598136b
--- /dev/null
+++ b/packages/backend/migration/1750729939704-FixAvatarUrl.js
@@ -0,0 +1,15 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+export class FixAvatarUrl1750729939704 {
+    name = 'FixAvatarUrl1750729939704'
+
+    async up(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "user" ALTER COLUMN "avatarUrl" TYPE character varying(1024)`);
+    }
+
+    async down(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "user" ALTER COLUMN "avatarUrl" TYPE character varying(512)`);
+    }
+}
diff --git a/packages/backend/src/models/User.ts b/packages/backend/src/models/User.ts
index baf4eefdf1..a6e9edcf5f 100644
--- a/packages/backend/src/models/User.ts
+++ b/packages/backend/src/models/User.ts
@@ -120,7 +120,7 @@ export class MiUser {
 
 	// avatarId が null になったとしてもこれが null でない可能性があるため、このフィールドを使うときは avatarId の non-null チェックをすること
 	@Column('varchar', {
-		length: 512, nullable: true,
+		length: 1024, nullable: true,
 	})
 	public avatarUrl: string | null;