diff --git a/Lombiq.Walkthroughs/Filters/WalkthroughsButtonFilter.cs b/Lombiq.Walkthroughs/Filters/WalkthroughsButtonFilter.cs
index d0d9ad8..66bda9d 100644
--- a/Lombiq.Walkthroughs/Filters/WalkthroughsButtonFilter.cs
+++ b/Lombiq.Walkthroughs/Filters/WalkthroughsButtonFilter.cs
@@ -7,7 +7,7 @@
 
 namespace Lombiq.Walkthroughs.Filters;
 
-public class WalkthroughsButtonFilter : IAsyncResultFilter
+public sealed class WalkthroughsButtonFilter : IAsyncResultFilter
 {
     private readonly IShapeFactory _shapeFactory;
     private readonly ILayoutAccessor _layoutAccessor;
diff --git a/Lombiq.Walkthroughs/Startup.cs b/Lombiq.Walkthroughs/Startup.cs
index ff06f34..be66014 100644
--- a/Lombiq.Walkthroughs/Startup.cs
+++ b/Lombiq.Walkthroughs/Startup.cs
@@ -12,7 +12,7 @@
 
 namespace Lombiq.Walkthroughs;
 
-public class Startup : StartupBase
+public sealed class Startup : StartupBase
 {
     public override void ConfigureServices(IServiceCollection services)
     {