diff --git a/client.go b/client.go
index 4740abba..a6d89338 100644
--- a/client.go
+++ b/client.go
@@ -1224,7 +1224,7 @@ func (cli *Client) SendMassagedStateEvent(ctx context.Context, roomID id.RoomID,
 }
 
 func (cli *Client) UpdateDelayedEvent(ctx context.Context, req *ReqUpdateDelayedEvent) (resp *RespUpdateDelayedEvent, err error) {
-	urlPath := cli.BuildClientURL("v1", "delayed_events", req.DelayID)
+	urlPath := cli.BuildClientURL("unstable", "org.matrix.msc4140", "delayed_events", req.DelayID)
 	_, err = cli.MakeRequest(ctx, http.MethodPut, urlPath, req, &resp)
 	return
 }