is8601 don't get passed in auth_token

I am getting this when using auth_token with memcache enabled :

swift Starting the S3 Token Authentication component
swift Started child 911
swift Starting the S3 Token Authentication component
swift Error: global name 'iso8601' is not defined:
Traceback (most recent call last):
  File "/shared/GIT/openstack/swift/swift/common/middleware/catch_errors.py", line 47, in __call__
    return self.app(env, my_start_response)
  File "/shared/GIT/openstack/swift/swift/common/middleware/healthcheck.py", line 38, in __call__
    return self.app(env, start_response)
  File "/shared/GIT/openstack/swift/swift/common/middleware/memcache.py", line 47, in __call__
    return self.app(env, start_response)
  File "/shared/GIT/openstack/swift/swift/common/middleware/swift3.py", line 460, in __call__
    return self.app(env, start_response)
  File "/shared/GIT/openstack/keystone/keystone/middleware/s3_token.py", line 63, in __call__
    return self.app(environ, start_response)
  File "/shared/GIT/openstack/keystone/keystone/middleware/auth_token.py", line 172, in __call__
    token_info = self._validate_user_token(user_token)
  File "/shared/GIT/openstack/keystone/keystone/middleware/auth_token.py", line 345, in _validate_user_token
    self._cache_put(user_token, data)
  File "/shared/GIT/openstack/keystone/keystone/middleware/auth_token.py", line 473, in _cache_put
    expires = iso8601.parse_date(timestamp)
NameError: global name 'iso8601' is not defined (txn: tx6607b461da42426eb057685b0e0dcd16)

iso8601 was properly imported in __init__() but I guess webob/wsgi don't pass the import to other methods (and due need a self. variable or a env variable to pass the import)