diff --git a/wikidata_ext.py b/wikidata_ext.py
index 51a5fa4..3f0c26c 100644
--- a/wikidata_ext.py
+++ b/wikidata_ext.py
@@ -6,7 +6,7 @@ import requests
 import json
 import logging
 
-REQUEST_SESSION = requests.Session()
+REQUEST_SESSION = None # TODO?
 
 def concept_uri(obj):
     assert isinstance(obj, wikidata.entity.Entity), obj
@@ -33,6 +33,7 @@ def fmt_triple_value(obj, prefer_obj = False):
 @ratelimit.sleep_and_retry
 def fetch_by_url(url, headers):
     logging.debug('Fetching: %s', url)
+    assert REQUEST_SESSION is not None, 'REQUEST_SESSION must be set, before calling fetch_by_url'
     response = REQUEST_SESSION.get(url, headers = headers)
     if response.status_code != 200:
         logging.error('Got %s error message: %s', response.status_code, response.text)