diff --git a/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs b/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs
index e3b74b65f12..fb1c487ca70 100644
--- a/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs
+++ b/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs
@@ -1439,10 +1439,10 @@ private ValueExpression CreateDeserializeValueExpression(
             {
                 { IsFrameworkType: true } when valueType.FrameworkType == typeof(Nullable<>) =>
                     ScmCodeModelGenerator.Instance.TypeFactory.DeserializeJsonValue(
-                        valueType.Arguments[0].FrameworkType, jsonElement, data,
+                        valueType.Arguments[0], jsonElement, data,
                         _mrwOptionsParameterSnippet, serializationFormat),
                 { IsFrameworkType: true } =>
-                    ScmCodeModelGenerator.Instance.TypeFactory.DeserializeJsonValue(valueType.FrameworkType,
+                    ScmCodeModelGenerator.Instance.TypeFactory.DeserializeJsonValue(valueType,
                         jsonElement, data, _mrwOptionsParameterSnippet,
                         serializationFormat),
                 { IsEnum: true } =>
diff --git a/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs b/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs
index 7089a0d2e4a..22f202f9210 100644
--- a/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs
+++ b/packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmMethodProviderCollection.cs
@@ -150,7 +150,7 @@ .. GetStackVariablesForReturnValueConversion(result, responseBodyType, isAsync,
                             Declare("element", jsonDocument.RootElement(), out var jsonElement),
                             Return(result.FromValue(
                                 ScmCodeModelGenerator.Instance.TypeFactory.DeserializeJsonValue(
-                                responseBodyType.FrameworkType,
+                                responseBodyType,
                                 jsonElement,
                                 data,
                                 ScmCodeModelGenerator.Instance.ModelSerializationExtensionsDefinition.WireOptionsField.As<ModelReaderWriterOptions>(),