diff --git a/src/Umbraco.Core/Services/ContentTypeServiceExtensions.cs b/src/Umbraco.Core/Services/ContentTypeServiceExtensions.cs
index fd8106707d..0a5cff6d4b 100644
--- a/src/Umbraco.Core/Services/ContentTypeServiceExtensions.cs
+++ b/src/Umbraco.Core/Services/ContentTypeServiceExtensions.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Umbraco.Core.Models;