Fetching data from binary cursor

Hi,

I am using Psycopg 2.7.1 from a Django application. To improve the
performance of some very large queries I want to test server-side binary
cursors and when I try to fetch results from it, I run into this error:

rows = cursor.fetchall()
ValueError: invalid literal for long() with base 10: ''

This is what I do:

from django.db import connection

cursor = connection.connection.cursor()
cursor.execute('''
DECLARE test_cursor BINARY CURSOR FOR
SELECT * FROM treenode
''')
cursor.execute("""FETCH 1 FROM test_cursor""")
rows = cursor.fetchall()

The cursor I get from Django (connection.connection.cursor()) is a
genuine Psycopg2 cursor:

> type(cursor)
psycopg2.extensions.cursor

Is there something I am doing wrong?

Thanks,
Tom