diff --git a/packages/knex/src/query/QueryBuilderHelper.ts b/packages/knex/src/query/QueryBuilderHelper.ts
index ca2ffec76551..ecbfd274a06f 100644
--- a/packages/knex/src/query/QueryBuilderHelper.ts
+++ b/packages/knex/src/query/QueryBuilderHelper.ts
@@ -395,10 +395,10 @@ export class QueryBuilderHelper {
       Utils.splitPrimaryKeys(field).forEach(f => {
         const direction = orderBy[k];
         const prop = this.getProperty(f, alias);
-        const noPrefix = prop && prop.persist === false;
+        const noPrefix = (prop && prop.persist === false) || QueryBuilderHelper.isCustomExpression(f);
         const order = Utils.isNumber<QueryOrderNumeric>(direction) ? QueryOrderNumeric[direction] : direction;
         const column = this.mapper(noPrefix ? f : `${alias}.${f}`, type);
-        const rawColumn = column.split('.').map(e => this.knex.ref(e)).join('.');
+        const rawColumn = Utils.isString(column) ? column.split('.').map(e => this.knex.ref(e)).join('.') : column;
 
         ret.push(`${rawColumn} ${order.toLowerCase()}`);
       });
diff --git a/tests/QueryBuilder.test.ts b/tests/QueryBuilder.test.ts
index 82b5864abdd9..10e50da5aba0 100644
--- a/tests/QueryBuilder.test.ts
+++ b/tests/QueryBuilder.test.ts
@@ -1403,6 +1403,12 @@ describe('QueryBuilder', () => {
     expect(qb.getQuery()).toEqual('select `e0`.* from `publisher2` as `e0` order by `e0`.`name` desc nulls last, `e0`.`type` asc nulls last');
   });
 
+  test('order by custom expression', async () => {
+    const qb = orm.em.createQueryBuilder(Publisher2);
+    qb.select('*').orderBy({ 'length(name)': QueryOrder.DESC, 'type': QueryOrder.ASC });
+    expect(qb.getQuery()).toEqual('select `e0`.* from `publisher2` as `e0` order by length(name) desc, `e0`.`type` asc');
+  });
+
   test('pg array operators', async () => {
     const pg = await MikroORM.init<PostgreSqlDriver>({
       entities: [Author2, Address2, Book2, BookTag2, Publisher2, Test2, BaseEntity2, Configuration2],