An inkjet pen has a body enclosing an ink reservoir and defining a vent aperture. A vent plug defining an elongated serpentine channel occupies the aperture. The plug may be cylindrical, with smaller diameter pilot ends to facilitate insertion. The serpentine channel may include several segments that alternate in direction, and which occupy a major portion of the plug surface away from an elongated spine surface portion that extends the length of the plug without interruption by the channel.