diff --git a/gwcelery/tasks/external_triggers.py b/gwcelery/tasks/external_triggers.py
index b4b238fbeca983aba0101f883bea3c6611ebe778..a7a746395067fcb2d547a06b739531b36f477249 100644
--- a/gwcelery/tasks/external_triggers.py
+++ b/gwcelery/tasks/external_triggers.py
@@ -299,10 +299,10 @@ def handle_grb_igwn_alert(alert):
         if _skymaps_are_ready(alert['object'], alert['data']['name'],
                               'compare'):
             # if both sky maps present and a coincidence, compare sky maps
-            superevent_id, ext_ids = _get_superevent_ext_ids(
-                graceid, alert['object'], 'compare')
+            superevent_id, ext_id = _get_superevent_ext_ids(
+                graceid, alert['object'], 'combine')
             superevent = gracedb.get_superevent(superevent_id)
-            gw_group = superevent['preferred_event_data']['group'] 
+            gw_group = superevent['preferred_event_data']['group']
             tl, th = raven._time_window(graceid, gw_group,
                                         [alert['object']['pipeline']],
                                         [alert['object']['search']])