diff --git a/sdk/src/Services/S3/Custom/AmazonS3Client.Custom.cs b/sdk/src/Services/S3/Custom/AmazonS3Client.Custom.cs
index 07fe925a9b9d..512dfd75910c 100644
--- a/sdk/src/Services/S3/Custom/AmazonS3Client.Custom.cs
+++ b/sdk/src/Services/S3/Custom/AmazonS3Client.Custom.cs
@@ -7,6 +7,7 @@
 using System.Threading.Tasks;
 using Amazon.S3.Model;
 using Amazon.S3.Model.Internal.MarshallTransformations;
+using Amazon.Runtime.Internal;
 using System.Threading;
 #pragma warning disable CS1570
 namespace Amazon.S3