Custom fields of the entity is not visible in the plugin

Hello All,

We have added a couple of custom of fields to the contact entity and added them to the form.
The new fields work fine. But when we try to get hold of the entity in the plugin presave using the generic Entity object,

Entity entity = (Entity)context.InputParameters["Target"];

we cant find the custom fields as a part of the entity object.
Should we typecast the generic entity to "contact" using a proxy class that's generated with  "CrmSvcUtil"?

Thanks & Regards,
Clement