diff --git a/src/spikeinterface/preprocessing/common_reference.py b/src/spikeinterface/preprocessing/common_reference.py
index 219854f340..c40aa11767 100644
--- a/src/spikeinterface/preprocessing/common_reference.py
+++ b/src/spikeinterface/preprocessing/common_reference.py
@@ -98,7 +98,9 @@ def __init__(
 
         # tranforms groups (ids) to groups (indices)
         if groups is not None:
-            groups = [self.ids_to_indices(g) for g in groups]
+            group_indices = [self.ids_to_indices(g) for g in groups]
+        else:
+            group_indices = None
         if ref_channel_ids is not None:
             ref_channel_inds = self.ids_to_indices(ref_channel_ids)
         else:
@@ -106,7 +108,7 @@ def __init__(
 
         for parent_segment in recording._recording_segments:
             rec_segment = CommonReferenceRecordingSegment(
-                parent_segment, reference, operator, groups, ref_channel_inds, local_radius, neighbors, dtype_
+                parent_segment, reference, operator, group_indices, ref_channel_inds, local_radius, neighbors, dtype_
             )
             self.add_recording_segment(rec_segment)
 
@@ -123,13 +125,21 @@ def __init__(
 
 class CommonReferenceRecordingSegment(BasePreprocessorSegment):
     def __init__(
-        self, parent_recording_segment, reference, operator, groups, ref_channel_inds, local_radius, neighbors, dtype
+        self,
+        parent_recording_segment,
+        reference,
+        operator,
+        group_indices,
+        ref_channel_inds,
+        local_radius,
+        neighbors,
+        dtype,
     ):
         BasePreprocessorSegment.__init__(self, parent_recording_segment)
 
         self.reference = reference
         self.operator = operator
-        self.groups = groups
+        self.group_indices = group_indices
         self.ref_channel_inds = ref_channel_inds
         self.local_radius = local_radius
         self.neighbors = neighbors
@@ -175,8 +185,8 @@ def get_traces(self, start_frame, end_frame, channel_indices):
     def _groups(self, channel_indices):
         selected_groups = []
         selected_channels = []
-        if self.groups:
-            for chan_inds in self.groups:
+        if self.group_indices:
+            for chan_inds in self.group_indices:
                 sel_inds = [ind for ind in channel_indices if ind in chan_inds]
                 # if no channels are in a group, do not return the group
                 if len(sel_inds) > 0: