diff --git a/src/libraries/Microsoft.Extensions.Logging.Abstractions/ref/Microsoft.Extensions.Logging.Abstractions.cs b/src/libraries/Microsoft.Extensions.Logging.Abstractions/ref/Microsoft.Extensions.Logging.Abstractions.cs
index 4e973443ef8257..cd1125477953f3 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Abstractions/ref/Microsoft.Extensions.Logging.Abstractions.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Abstractions/ref/Microsoft.Extensions.Logging.Abstractions.cs
@@ -177,7 +177,7 @@ public readonly partial struct LogEntry<TState>
         public Microsoft.Extensions.Logging.LogLevel LogLevel { get { throw null; } }
         public TState State { get { throw null; } }
     }
-    public partial class NullLogger : Microsoft.Extensions.Logging.ILogger
+    public sealed partial class NullLogger : Microsoft.Extensions.Logging.ILogger
     {
         internal NullLogger() { }
         public static Microsoft.Extensions.Logging.Abstractions.NullLogger Instance { get { throw null; } }
diff --git a/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/NullLogger.cs b/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/NullLogger.cs
index e2b1cd8b264eb8..d77a41315a0ec7 100644
--- a/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/NullLogger.cs
+++ b/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/NullLogger.cs
@@ -8,7 +8,7 @@ namespace Microsoft.Extensions.Logging.Abstractions
     /// <summary>
     /// Minimalistic logger that does nothing.
     /// </summary>
-    public class NullLogger : ILogger
+    public sealed class NullLogger : ILogger
     {
         /// <summary>
         /// Returns the shared instance of <see cref="NullLogger"/>.