diff --git a/MachineTool/DemoBuildMachineTool.cs b/MachineTool/DemoBuildMachineTool.cs
index 18fb746..38467d2 100644
--- a/MachineTool/DemoBuildMachineTool.cs
+++ b/MachineTool/DemoBuildMachineTool.cs
@@ -23,9 +23,15 @@ namespace Sample.MachineTool
     /// </remarks>
     public class DemoBuildMachineTool : IGetCodeXyzabcMachineTool
     {
-        static DemoBuildMachineTool()
+        /// <summary>
+        /// Registers this type's deserializer with the given <see cref="XFactory"/>
+        /// (or <see cref="XFactory.Default"/> when <paramref name="factory"/> is
+        /// <c>null</c>). Idempotent.
+        /// </summary>
+        public static void Reg(XFactory factory = null)
         {
-            XFactory.Generators.Add(XName, (xml, baseDirectory, relFile, progress, res) => new DemoBuildMachineTool());
+            factory ??= XFactory.Default;
+            factory.Generators.TryAdd(XName, (xml, baseDirectory, relFile, progress, res) => new DemoBuildMachineTool());
         }
         /// <summary>
         /// Generates an XYZ-ABC machine tool instance from embedded resources.