Fix Python – How do I get Pyflakes to ignore a statement?

A lot of our modules start with:
try:
import json
except ImportError:
from django.utils import simplejson as json # Python 2.4 fallback.

…and it’s the only Pyflakes warning in the entire file:
foo/bar.py:14: redefinition of unused ‘json’ from line 12

How can I get Pyflakes to ignore this?
(Normally I’d go read the docs but the link is….