--- a/taskcluster/taskgraph/util/taskcluster.py
+++ b/taskcluster/taskgraph/util/taskcluster.py
@@ -78,17 +78,22 @@ def get_index_url(index_path, use_proxy=
     if use_proxy:
         INDEX_URL = 'http://taskcluster/index/v1/task/{}'
     else:
         INDEX_URL = 'https://index.taskcluster.net/v1/task/{}'
     return INDEX_URL.format(index_path)
 
 
 def find_task_id(index_path, use_proxy=False):
-    response = _do_request(get_index_url(index_path, use_proxy))
+    try:
+        response = _do_request(get_index_url(index_path, use_proxy))
+    except requests.exceptions.HTTPError as e:
+        if e.response.status_code == 404:
+            raise KeyError("index path {} not found".format(index_path))
+        raise
     return response.json()['taskId']
 
 
 def get_artifact_from_index(index_path, artifact_path, use_proxy=False):
     full_path = index_path + '/artifacts/' + artifact_path
     response = _do_request(get_index_url(full_path, use_proxy))
     return _handle_artifact(full_path, response)