diff --git a/src/proto_nd_flow/reco/charge/raw_event_generator.py b/src/proto_nd_flow/reco/charge/raw_event_generator.py
index 82050bad..e4a28911 100644
--- a/src/proto_nd_flow/reco/charge/raw_event_generator.py
+++ b/src/proto_nd_flow/reco/charge/raw_event_generator.py
@@ -432,8 +432,8 @@ def next(self):
             # write mc data to file
             mc_assn = (np.concatenate(event_mc_assn, axis=0)
                        if len(event_mc_assn) else np.full((0,), -1, dtype=self.mc_assn.dtype))
-            mc_assn_mask = (mc_assn['track_ids'] == -1) | (mc_assn['fraction'] == 0.)
-            event_tracks = ma.array(mc_assn['track_ids'], mask=mc_assn_mask)
+            mc_assn_mask = (mc_assn['segment_ids'] == -1) | (mc_assn['fraction'] == 0.)
+            event_tracks = ma.array(mc_assn['segment_ids'], mask=mc_assn_mask)
             event_packet_fraction = ma.array(mc_assn['fraction'], mask=mc_assn_mask)
 
             # set up packet references