diff --git a/src/Autofac/ContainerBuilder.cs b/src/Autofac/ContainerBuilder.cs
index 8aa61e722..c3fc5ea9e 100644
--- a/src/Autofac/ContainerBuilder.cs
+++ b/src/Autofac/ContainerBuilder.cs
@@ -58,7 +58,7 @@ namespace Autofac
     /// via extension methods in <see cref="RegistrationExtensions"/>.</remarks>
     /// <seealso cref="IContainer"/>
     /// <see cref="RegistrationExtensions"/>
-    public class ContainerBuilder
+    public sealed class ContainerBuilder
     {
         private readonly IList<DeferredCallback> _configurationCallbacks = new List<DeferredCallback>();
         private BuildCallbackService? _buildCallbacks;