diff --git a/packages/server/src/db.migrations.test.ts b/packages/server/src/db.migrations.test.ts
index daa215adcf..a5e2d09cdd 100644
--- a/packages/server/src/db.migrations.test.ts
+++ b/packages/server/src/db.migrations.test.ts
@@ -33,6 +33,7 @@ describe('db.migrations', () => {
 			'20220121172409_email_recipient_default',
 			'20240413141308_changes_optimization',
 			'20250219183745_changes_optimization',
+			'20251107113000_fix_delta_performance',
 		];
 
 		let startProcessing = false;
diff --git a/packages/server/src/migrations/20251107113000_fix_delta_performance.ts b/packages/server/src/migrations/20251107113000_fix_delta_performance.ts
new file mode 100644
index 0000000000..d82770bf32
--- /dev/null
+++ b/packages/server/src/migrations/20251107113000_fix_delta_performance.ts
@@ -0,0 +1,27 @@
+import { DbConnection, isPostgres } from '../db';
+
+// CREATE INDEX CONCURRENTLY cannot run within a transaction
+export const config = { transaction: false };
+
+export const up = async (db: DbConnection) => {
+	if (isPostgres(db)) {
+		// This is to optimize the sub-query in ChangeModel::changesForUserQuery() which retrieves
+		// the item creations and deletions. Having `item_id` first in the index helps PostgreSQL
+		// quickly find all rows in `changes` that belong to a specific `item_id`. We also filter it
+		// to `type = 2` (updates) because finding the changes for other types is done in a
+		// different query and is much easier.
+		await db.raw('CREATE INDEX CONCURRENTLY IF NOT EXISTS changes_item_id_counter_type2_index ON changes (item_id, counter) WHERE type = 2');
+
+		// Drop the old counter-only index. If it remains, the planner wrongly prefers it because it
+		// appears ideal for `ORDER BY counter`, but in reality it forces Postgres to scan millions
+		// of rows to find matching item_ids.
+		await db.raw('DROP INDEX CONCURRENTLY IF EXISTS changes_type2_counter_idx');
+	}
+};
+
+export const down = async (db: DbConnection) => {
+	if (isPostgres(db)) {
+		await db.raw('DROP INDEX CONCURRENTLY IF EXISTS changes_item_id_counter_type2_index');
+		await db.raw('CREATE INDEX CONCURRENTLY IF NOT EXISTS changes_type2_counter_idx ON changes (counter) WHERE type = 2');
+	}
+};