diff --git a/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator.UnitTests/MethodExtensionsTests.cs b/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator.UnitTests/MethodExtensionsTests.cs
index 664ba11307..55514bc488 100644
--- a/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator.UnitTests/MethodExtensionsTests.cs
+++ b/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator.UnitTests/MethodExtensionsTests.cs
@@ -136,6 +136,38 @@ public void StripsDocs()
 
                 Assert.Equal(expected, actual, ignoreLineEndingDifferences: true);
             }
+
+            [Fact(DisplayName = _Prefix + nameof(PreservesOptionality))]
+            public void PreservesOptionality()
+            {
+                Method method = new Method
+                (
+                    isProtected: false,
+                    isAbstract: false,
+                    name: "myMethod",
+                    parameters: new[]
+                    {
+                        new Parameter
+                        (
+                            name: "myParam1",
+                            type: new TypeReference("myParamTypeFqn1")
+                        ),
+                        new Parameter
+                        (
+                            name: "myParam2",
+                            type: new TypeReference("myParamTypeFqn2"),
+                            isOptional: true
+                        )
+                    }
+                );
+
+                SyntaxToken token = method.GetParametersJsonSyntaxToken();
+
+                string actual = token.ToString();
+                string expected = @"""[{\""name\"":\""myParam1\"",\""type\"":{\""fqn\"":\""myParamTypeFqn1\""}},{\""name\"":\""myParam2\"",\""type\"":{\""fqn\"":\""myParamTypeFqn2\""},\""optional\"":true}]""";
+
+                Assert.Equal(expected, actual, ignoreLineEndingDifferences: true);
+            }
         }
     }
 }
diff --git a/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/CallableExtensions.cs b/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/CallableExtensions.cs
index 7c5d013dca..31a1ad4aa5 100644
--- a/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/CallableExtensions.cs
+++ b/packages/jsii-dotnet-generator/src/Amazon.JSII.Generator/CallableExtensions.cs
@@ -51,7 +51,7 @@ public static SyntaxToken GetParametersJsonSyntaxToken(this Callable callable)
         {
             // Strip docs before serializing.
             Parameter[] parameters = (callable?.Parameters ?? Enumerable.Empty<Parameter>())
-                .Select(p => new Parameter(p.Name, p.Type))
+                .Select(p => new Parameter(name: p.Name, type: p.Type, isOptional: p.IsOptional, isVariadic: p.IsVariadic))
                 .ToArray();
 
             return SF.Literal(JsonConvert.SerializeObject(parameters, SerializerSettings));
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/Calculator.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/Calculator.cs
index be7f166dd4..471950846a 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/Calculator.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/Calculator.cs
@@ -6,7 +6,7 @@
 namespace Amazon.JSII.Tests.CalculatorNamespace
 {
     /// <summary>A calculator which maintains a current value and allows adding operations.</summary>
-    [JsiiClass(nativeType: typeof(Calculator), fullyQualifiedName: "jsii-calc.Calculator", parametersJson: "[{\"name\":\"props\",\"type\":{\"fqn\":\"jsii-calc.CalculatorProps\"}}]")]
+    [JsiiClass(nativeType: typeof(Calculator), fullyQualifiedName: "jsii-calc.Calculator", parametersJson: "[{\"name\":\"props\",\"type\":{\"fqn\":\"jsii-calc.CalculatorProps\"},\"optional\":true}]")]
     public class Calculator : CompositeOperation_
     {
         public Calculator(ICalculatorProps props): base(new DeputyProps(new object[]{props}))
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DefaultedConstructorArgument.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DefaultedConstructorArgument.cs
index 08874c3b0d..f5575e39ee 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DefaultedConstructorArgument.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DefaultedConstructorArgument.cs
@@ -3,7 +3,7 @@
 
 namespace Amazon.JSII.Tests.CalculatorNamespace
 {
-    [JsiiClass(nativeType: typeof(DefaultedConstructorArgument), fullyQualifiedName: "jsii-calc.DefaultedConstructorArgument", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"number\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg3\",\"type\":{\"primitive\":\"date\"}}]")]
+    [JsiiClass(nativeType: typeof(DefaultedConstructorArgument), fullyQualifiedName: "jsii-calc.DefaultedConstructorArgument", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"number\"},\"optional\":true},{\"name\":\"arg2\",\"type\":{\"primitive\":\"string\"},\"optional\":true},{\"name\":\"arg3\",\"type\":{\"primitive\":\"date\"},\"optional\":true}]")]
     public class DefaultedConstructorArgument : DeputyBase
     {
         public DefaultedConstructorArgument(double? arg1, string arg2, DateTime? arg3): base(new DeputyProps(new object[]{arg1, arg2, arg3}))
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DoNotRecognizeAnyAsOptional.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DoNotRecognizeAnyAsOptional.cs
index 0e8c2b0012..fcf8be137c 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DoNotRecognizeAnyAsOptional.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DoNotRecognizeAnyAsOptional.cs
@@ -18,7 +18,7 @@ protected DoNotRecognizeAnyAsOptional(DeputyProps props): base(props)
         {
         }
 
-        [JsiiMethod(name: "method", parametersJson: "[{\"name\":\"_requiredAny\",\"type\":{\"primitive\":\"any\"}},{\"name\":\"_optionalAny\",\"type\":{\"primitive\":\"any\"}},{\"name\":\"_optionalString\",\"type\":{\"primitive\":\"string\"}}]")]
+        [JsiiMethod(name: "method", parametersJson: "[{\"name\":\"_requiredAny\",\"type\":{\"primitive\":\"any\"}},{\"name\":\"_optionalAny\",\"type\":{\"primitive\":\"any\"},\"optional\":true},{\"name\":\"_optionalString\",\"type\":{\"primitive\":\"string\"},\"optional\":true}]")]
         public virtual void Method(object _requiredAny, object _optionalAny, string _optionalString)
         {
             InvokeInstanceVoidMethod(new object[]{_requiredAny, _optionalAny, _optionalString});
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DocumentedClass.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DocumentedClass.cs
index e6e1ba0344..3cb3f2bade 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DocumentedClass.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DocumentedClass.cs
@@ -32,7 +32,7 @@ protected DocumentedClass(DeputyProps props): base(props)
         /// This will print out a friendly greeting intended for
         /// the indicated person.
         /// </remarks>
-        [JsiiMethod(name: "greet", returnsJson: "{\"type\":{\"primitive\":\"number\"}}", parametersJson: "[{\"name\":\"greetee\",\"type\":{\"fqn\":\"jsii-calc.Greetee\"}}]")]
+        [JsiiMethod(name: "greet", returnsJson: "{\"type\":{\"primitive\":\"number\"}}", parametersJson: "[{\"name\":\"greetee\",\"type\":{\"fqn\":\"jsii-calc.Greetee\"},\"optional\":true}]")]
         public virtual double Greet(IGreetee greetee)
         {
             return InvokeInstanceMethod<double>(new object[]{greetee});
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DontComplainAboutVariadicAfterOptional.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DontComplainAboutVariadicAfterOptional.cs
index 6a79257436..f4fd0ffa5b 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DontComplainAboutVariadicAfterOptional.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/DontComplainAboutVariadicAfterOptional.cs
@@ -17,7 +17,7 @@ protected DontComplainAboutVariadicAfterOptional(DeputyProps props): base(props)
         {
         }
 
-        [JsiiMethod(name: "optionalAndVariadic", returnsJson: "{\"type\":{\"primitive\":\"string\"}}", parametersJson: "[{\"name\":\"optional\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"things\",\"type\":{\"primitive\":\"string\"}}]")]
+        [JsiiMethod(name: "optionalAndVariadic", returnsJson: "{\"type\":{\"primitive\":\"string\"}}", parametersJson: "[{\"name\":\"optional\",\"type\":{\"primitive\":\"string\"},\"optional\":true},{\"name\":\"things\",\"variadic\":true,\"type\":{\"primitive\":\"string\"}}]")]
         public virtual string OptionalAndVariadic(string optional, string things)
         {
             return InvokeInstanceMethod<string>(new object[]{optional, things});
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/IIInterfaceWithOptionalMethodArguments.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/IIInterfaceWithOptionalMethodArguments.cs
index 0654eb191d..874af8c98c 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/IIInterfaceWithOptionalMethodArguments.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/IIInterfaceWithOptionalMethodArguments.cs
@@ -6,7 +6,7 @@ namespace Amazon.JSII.Tests.CalculatorNamespace
     [JsiiInterface(nativeType: typeof(IIInterfaceWithOptionalMethodArguments), fullyQualifiedName: "jsii-calc.IInterfaceWithOptionalMethodArguments")]
     public interface IIInterfaceWithOptionalMethodArguments
     {
-        [JsiiMethod(name: "hello", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"number\"}}]")]
+        [JsiiMethod(name: "hello", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"number\"},\"optional\":true}]")]
         void Hello(string arg1, double? arg2);
     }
 }
\ No newline at end of file
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/IInterfaceWithOptionalMethodArgumentsProxy.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/IInterfaceWithOptionalMethodArgumentsProxy.cs
index 96cb738037..40ae97b5c0 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/IInterfaceWithOptionalMethodArgumentsProxy.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/IInterfaceWithOptionalMethodArgumentsProxy.cs
@@ -10,7 +10,7 @@ private IInterfaceWithOptionalMethodArgumentsProxy(ByRefValue reference): base(r
         {
         }
 
-        [JsiiMethod(name: "hello", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"number\"}}]")]
+        [JsiiMethod(name: "hello", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"number\"},\"optional\":true}]")]
         public void Hello(string arg1, double? arg2)
         {
             InvokeInstanceVoidMethod(new object[]{arg1, arg2});
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/NullShouldBeTreatedAsUndefined.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/NullShouldBeTreatedAsUndefined.cs
index b563485362..8430bc9d34 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/NullShouldBeTreatedAsUndefined.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/NullShouldBeTreatedAsUndefined.cs
@@ -3,7 +3,7 @@
 namespace Amazon.JSII.Tests.CalculatorNamespace
 {
     /// <summary>jsii#282, aws-cdk#157: null should be treated as "undefined".</summary>
-    [JsiiClass(nativeType: typeof(NullShouldBeTreatedAsUndefined), fullyQualifiedName: "jsii-calc.NullShouldBeTreatedAsUndefined", parametersJson: "[{\"name\":\"_param1\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"optional\",\"type\":{\"primitive\":\"any\"}}]")]
+    [JsiiClass(nativeType: typeof(NullShouldBeTreatedAsUndefined), fullyQualifiedName: "jsii-calc.NullShouldBeTreatedAsUndefined", parametersJson: "[{\"name\":\"_param1\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"optional\",\"type\":{\"primitive\":\"any\"},\"optional\":true}]")]
     public class NullShouldBeTreatedAsUndefined : DeputyBase
     {
         public NullShouldBeTreatedAsUndefined(string _param1, object optional): base(new DeputyProps(new object[]{_param1, optional}))
@@ -25,7 +25,7 @@ public virtual string ChangeMeToUndefined
             set => SetInstanceProperty(value);
         }
 
-        [JsiiMethod(name: "giveMeUndefined", parametersJson: "[{\"name\":\"value\",\"type\":{\"primitive\":\"any\"}}]")]
+        [JsiiMethod(name: "giveMeUndefined", parametersJson: "[{\"name\":\"value\",\"type\":{\"primitive\":\"any\"},\"optional\":true}]")]
         public virtual void GiveMeUndefined(object value)
         {
             InvokeInstanceVoidMethod(new object[]{value});
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/OptionalConstructorArgument.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/OptionalConstructorArgument.cs
index 0149af9852..9964cf0c01 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/OptionalConstructorArgument.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/OptionalConstructorArgument.cs
@@ -3,7 +3,7 @@
 
 namespace Amazon.JSII.Tests.CalculatorNamespace
 {
-    [JsiiClass(nativeType: typeof(OptionalConstructorArgument), fullyQualifiedName: "jsii-calc.OptionalConstructorArgument", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"number\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg3\",\"type\":{\"primitive\":\"date\"}}]")]
+    [JsiiClass(nativeType: typeof(OptionalConstructorArgument), fullyQualifiedName: "jsii-calc.OptionalConstructorArgument", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"number\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg3\",\"type\":{\"primitive\":\"date\"},\"optional\":true}]")]
     public class OptionalConstructorArgument : DeputyBase
     {
         public OptionalConstructorArgument(double arg1, string arg2, DateTime? arg3): base(new DeputyProps(new object[]{arg1, arg2, arg3}))
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/OptionalStructConsumer.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/OptionalStructConsumer.cs
index 13697c4d04..2ea6132c81 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/OptionalStructConsumer.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/OptionalStructConsumer.cs
@@ -2,7 +2,7 @@
 
 namespace Amazon.JSII.Tests.CalculatorNamespace
 {
-    [JsiiClass(nativeType: typeof(OptionalStructConsumer), fullyQualifiedName: "jsii-calc.OptionalStructConsumer", parametersJson: "[{\"name\":\"optionalStruct\",\"type\":{\"fqn\":\"jsii-calc.OptionalStruct\"}}]")]
+    [JsiiClass(nativeType: typeof(OptionalStructConsumer), fullyQualifiedName: "jsii-calc.OptionalStructConsumer", parametersJson: "[{\"name\":\"optionalStruct\",\"type\":{\"fqn\":\"jsii-calc.OptionalStruct\"},\"optional\":true}]")]
     public class OptionalStructConsumer : DeputyBase
     {
         public OptionalStructConsumer(IOptionalStruct optionalStruct): base(new DeputyProps(new object[]{optionalStruct}))
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/RuntimeTypeChecking.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/RuntimeTypeChecking.cs
index 657eb4de71..eff77f309d 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/RuntimeTypeChecking.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/RuntimeTypeChecking.cs
@@ -18,20 +18,20 @@ protected RuntimeTypeChecking(DeputyProps props): base(props)
         {
         }
 
-        [JsiiMethod(name: "methodWithDefaultedArguments", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"number\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg3\",\"type\":{\"primitive\":\"date\"}}]")]
+        [JsiiMethod(name: "methodWithDefaultedArguments", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"number\"},\"optional\":true},{\"name\":\"arg2\",\"type\":{\"primitive\":\"string\"},\"optional\":true},{\"name\":\"arg3\",\"type\":{\"primitive\":\"date\"},\"optional\":true}]")]
         public virtual void MethodWithDefaultedArguments(double? arg1, string arg2, DateTime? arg3)
         {
             InvokeInstanceVoidMethod(new object[]{arg1, arg2, arg3});
         }
 
-        [JsiiMethod(name: "methodWithOptionalAnyArgument", parametersJson: "[{\"name\":\"arg\",\"type\":{\"primitive\":\"any\"}}]")]
+        [JsiiMethod(name: "methodWithOptionalAnyArgument", parametersJson: "[{\"name\":\"arg\",\"type\":{\"primitive\":\"any\"},\"optional\":true}]")]
         public virtual void MethodWithOptionalAnyArgument(object arg)
         {
             InvokeInstanceVoidMethod(new object[]{arg});
         }
 
         /// <summary>Used to verify verification of number of method arguments.</summary>
-        [JsiiMethod(name: "methodWithOptionalArguments", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"number\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg3\",\"type\":{\"primitive\":\"date\"}}]")]
+        [JsiiMethod(name: "methodWithOptionalArguments", parametersJson: "[{\"name\":\"arg1\",\"type\":{\"primitive\":\"number\"}},{\"name\":\"arg2\",\"type\":{\"primitive\":\"string\"}},{\"name\":\"arg3\",\"type\":{\"primitive\":\"date\"},\"optional\":true}]")]
         public virtual void MethodWithOptionalArguments(double arg1, string arg2, DateTime? arg3)
         {
             InvokeInstanceVoidMethod(new object[]{arg1, arg2, arg3});
diff --git a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/VariadicMethod.cs b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/VariadicMethod.cs
index 3e373213c3..fa02b7e62b 100644
--- a/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/VariadicMethod.cs
+++ b/packages/jsii-pacmak/test/expected.jsii-calc/dotnet/Amazon.JSII.Tests.CalculatorPackageId/Amazon/JSII/Tests/CalculatorNamespace/VariadicMethod.cs
@@ -2,7 +2,7 @@
 
 namespace Amazon.JSII.Tests.CalculatorNamespace
 {
-    [JsiiClass(nativeType: typeof(VariadicMethod), fullyQualifiedName: "jsii-calc.VariadicMethod", parametersJson: "[{\"name\":\"prefix\",\"type\":{\"primitive\":\"number\"}}]")]
+    [JsiiClass(nativeType: typeof(VariadicMethod), fullyQualifiedName: "jsii-calc.VariadicMethod", parametersJson: "[{\"name\":\"prefix\",\"variadic\":true,\"type\":{\"primitive\":\"number\"}}]")]
     public class VariadicMethod : DeputyBase
     {
         public VariadicMethod(double prefix): base(new DeputyProps(new object[]{prefix}))
@@ -19,7 +19,7 @@ protected VariadicMethod(DeputyProps props): base(props)
 
         /// <param name = "first">the first element of the array to be returned (after the `prefix` provided at construction time).</param>
         /// <param name = "others">other elements to be included in the array.</param>
-        [JsiiMethod(name: "asArray", returnsJson: "{\"type\":{\"collection\":{\"kind\":\"array\",\"elementtype\":{\"primitive\":\"number\"}}}}", parametersJson: "[{\"name\":\"first\",\"type\":{\"primitive\":\"number\"}},{\"name\":\"others\",\"type\":{\"primitive\":\"number\"}}]")]
+        [JsiiMethod(name: "asArray", returnsJson: "{\"type\":{\"collection\":{\"kind\":\"array\",\"elementtype\":{\"primitive\":\"number\"}}}}", parametersJson: "[{\"name\":\"first\",\"type\":{\"primitive\":\"number\"}},{\"name\":\"others\",\"variadic\":true,\"type\":{\"primitive\":\"number\"}}]")]
         public virtual double[] AsArray(double first, double others)
         {
             return InvokeInstanceMethod<double[]>(new object[]{first, others});