In some examples, a feedthrough assembly for a medical device may include a ferrule. The ferrule defines an aperture extending through the ferrule from an outer end surface defined by the ferrule to an end inner end surface defined by the ferrule. The aperture includes a first portion having a first diameter and a second portion having a second diameter less than the first diameter. The aperture defines a longitudinal axis extending therethrough and the ferrule defines a ledge between the first and second portions of the aperture that extends radially inward toward the longitudinal axis. The feedthrough assembly further may include a conductive pin within the aperture and an insulating member surrounding at least a portion of the pin. The insulating member may electrically insulate the conductive pin from the ferrule, and the ledge and a surface of the insulating member adjacent the ledge may define a space therebetween.