GeoDjango: Geographic query causes segmentation fault

Question

On Django development server with SpatiaLite, I am trying to do a basic geographic query:

Location.objects.filter(geom__within=loc.geom)

This causes a Segmentation error and the server dies. loc is an instance of the Location model:

from django.contrib.gis.db import models

class Location(models.Model):
    geom = models.GeometryField()

    objects = models.GeoManager()

What do you think might be wrong?