diff --git a/src/CommandLine/OptionAttribute.cs b/src/CommandLine/OptionAttribute.cs
index 6ae51dac..2727b5a8 100644
--- a/src/CommandLine/OptionAttribute.cs
+++ b/src/CommandLine/OptionAttribute.cs
@@ -10,7 +10,7 @@ namespace CommandLine
     /// Models an option specification.
     /// </summary>
     [AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
-    public sealed class OptionAttribute : BaseAttribute
+    public class OptionAttribute : BaseAttribute
     {
         private readonly string longName;
         private readonly string shortName;