diff --git a/SlackNet/WebApi/ChatApi.cs b/SlackNet/WebApi/ChatApi.cs
index 4be7631..82026b6 100644
--- a/SlackNet/WebApi/ChatApi.cs
+++ b/SlackNet/WebApi/ChatApi.cs
@@ -221,6 +221,7 @@ public Task<PostMessageResponse> PostEphemeral(string userId, Message message, C
                     { "attachments", message.Attachments },
                     { "blocks", message.Blocks },
                     { "link_names", message.LinkNames },
+                    { "thread_ts", message.ThreadTs },
                     { "parse", message.Parse }
                 },
             cancellationToken);
@@ -281,4 +282,4 @@ public Task<MessageUpdateResponse> Update(MessageUpdate messageUpdate, Cancellat
                     { "file_ids", messageUpdate.FileIds }
                 },
             cancellationToken);
-}
\ No newline at end of file
+}