diff --git a/src/Webserver.API/Services/ServerCertificateCallback.cs b/src/Webserver.API/Services/ServerCertificateCallback.cs
index 80d5a58..859ff71 100644
--- a/src/Webserver.API/Services/ServerCertificateCallback.cs
+++ b/src/Webserver.API/Services/ServerCertificateCallback.cs
@@ -18,11 +18,13 @@ public class ServerCertificateCallback
         /// <summary>
         /// Gets or sets custom server certificate callback.
         /// </summary>
+#nullable enable
         public static Func<HttpRequestMessage, X509Certificate2, X509Chain, SslPolicyErrors, bool>? CertificateCallback
         {
             get;
             set;
         }
+#nullable disable
     }
 }
 #endif
\ No newline at end of file