diff --git a/backend/src/Squidex/Areas/Api/Controllers/Schemas/Models/SchemaPropertiesDto.cs b/backend/src/Squidex/Areas/Api/Controllers/Schemas/Models/SchemaPropertiesDto.cs
index 58fd628b5..8deab5021 100644
--- a/backend/src/Squidex/Areas/Api/Controllers/Schemas/Models/SchemaPropertiesDto.cs
+++ b/backend/src/Squidex/Areas/Api/Controllers/Schemas/Models/SchemaPropertiesDto.cs
@@ -5,7 +5,7 @@
 //  All rights reserved. Licensed under the MIT license.
 // ==========================================================================
 
-using System.Collections.Immutable;
+using Squidex.Infrastructure.Collections;
 using Squidex.Infrastructure.Validation;
 
 namespace Squidex.Areas.Api.Controllers.Schemas.Models