diff --git a/NuRadioReco/detector/detector_base.py b/NuRadioReco/detector/detector_base.py
index 32519116d..edf85cb4c 100644
--- a/NuRadioReco/detector/detector_base.py
+++ b/NuRadioReco/detector/detector_base.py
@@ -951,7 +951,7 @@ def get_antenna_model(self, station_id, channel_id, zenith=None):
 
     def get_channel_group_id(self, station_id, channel_id):
         """
-        returns the group ID of a channel
+        returns the group ID of a channel. If the channel has no group ID, the channel ID is returned.
 
         Parameters
         ----------