diff --git a/spikeinterface_gui/controller.py b/spikeinterface_gui/controller.py
index 3ddea2d..e150888 100644
--- a/spikeinterface_gui/controller.py
+++ b/spikeinterface_gui/controller.py
@@ -600,7 +600,7 @@ def set_visible_unit_ids(self, visible_unit_ids):
 
     def get_visible_unit_ids(self):
         """Get list of visible unit_ids"""
-        return self._visible_unit_ids
+        return list(self._visible_unit_ids)
 
     def get_visible_unit_indices(self):
         """Get list of indices of visible units"""