diff --git a/src/spikeinterface/core/unitsaggregationsorting.py b/src/spikeinterface/core/unitsaggregationsorting.py
index df5a5589e8..647854406a 100644
--- a/src/spikeinterface/core/unitsaggregationsorting.py
+++ b/src/spikeinterface/core/unitsaggregationsorting.py
@@ -34,7 +34,8 @@ def __init__(self, sorting_list, renamed_unit_ids=None):
             )
             unit_ids = list(renamed_unit_ids)
         else:
-            all_ids_are_same_type = np.unique([sort.get_unit_ids().dtype for sort in sorting_list]).size == 1
+            unit_ids_dtypes = [sort.get_unit_ids().dtype for sort in sorting_list]
+            all_ids_are_same_type = np.unique(unit_ids_dtypes).size == 1
             all_units_ids_are_unique = False
             if all_ids_are_same_type:
                 combined_ids = np.concatenate([sort.get_unit_ids() for sort in sorting_list])
@@ -44,7 +45,10 @@ def __init__(self, sorting_list, renamed_unit_ids=None):
                 unit_ids = combined_ids
             else:
                 default_unit_ids = [str(i) for i in range(num_all_units)]
-                unit_ids = default_unit_ids
+                if all_ids_are_same_type and np.issubdtype(unit_ids_dtypes[0], np.integer):
+                    unit_ids = np.arange(num_all_units, dtype=dtype)
+                else:
+                    unit_ids = default_unit_ids
 
         # unit map maps unit ids that are used to get spike trains
         u_id = 0