diff --git a/src/Spectre.Console/Cli/Internal/Modelling/CommandModelBuilder.cs b/src/Spectre.Console/Cli/Internal/Modelling/CommandModelBuilder.cs
index 585da75..76fc323 100644
--- a/src/Spectre.Console/Cli/Internal/Modelling/CommandModelBuilder.cs
+++ b/src/Spectre.Console/Cli/Internal/Modelling/CommandModelBuilder.cs
@@ -233,7 +233,7 @@ namespace Spectre.Console.Cli
 
         private static ParameterKind GetParameterKind(Type type)
         {
-            if (type == typeof(bool))
+            if (type == typeof(bool) || type == typeof(bool?))
             {
                 return ParameterKind.Flag;
             }