diff --git a/src/spikeinterface/core/tests/test_unitsaggregationsorting.py b/src/spikeinterface/core/tests/test_unitsaggregationsorting.py
index b6cb479c7d..09b8affe55 100644
--- a/src/spikeinterface/core/tests/test_unitsaggregationsorting.py
+++ b/src/spikeinterface/core/tests/test_unitsaggregationsorting.py
@@ -5,6 +5,7 @@
 
 from spikeinterface.core import NpzSortingExtractor
 from spikeinterface.core import create_sorting_npz
+from spikeinterface.core import generate_sorting
 
 
 def test_unitsaggregationsorting(create_cache_folder):
@@ -92,5 +93,42 @@ def test_unitsaggregationsorting(create_cache_folder):
     print(sorting_agg_prop.get_property("brain_area"))
 
 
+def test_unit_aggregation_preserve_ids():
+
+    sorting1 = generate_sorting(num_units=3)
+    sorting1 = sorting1.rename_units(new_unit_ids=["unit1", "unit2", "unit3"])
+
+    sorting2 = generate_sorting(num_units=3)
+    sorting2 = sorting2.rename_units(new_unit_ids=["unit4", "unit5", "unit6"])
+
+    aggregated_sorting = aggregate_units([sorting1, sorting2])
+    assert aggregated_sorting.get_num_units() == 6
+    assert list(aggregated_sorting.get_unit_ids()) == ["unit1", "unit2", "unit3", "unit4", "unit5", "unit6"]
+
+
+def test_unit_aggregation_does_not_preserve_ids_if_not_unique():
+    sorting1 = generate_sorting(num_units=3)
+    sorting1 = sorting1.rename_units(new_unit_ids=["unit1", "unit2", "unit3"])
+
+    sorting2 = generate_sorting(num_units=3)
+    sorting2 = sorting2.rename_units(new_unit_ids=["unit1", "unit2", "unit3"])
+
+    aggregated_sorting = aggregate_units([sorting1, sorting2])
+    assert aggregated_sorting.get_num_units() == 6
+    assert list(aggregated_sorting.get_unit_ids()) == ["0", "1", "2", "3", "4", "5"]
+
+
+def test_unit_aggregation_does_not_preserve_ids_not_the_same_type():
+    sorting1 = generate_sorting(num_units=3)
+    sorting1 = sorting1.rename_units(new_unit_ids=["unit1", "unit2", "unit3"])
+
+    sorting2 = generate_sorting(num_units=2)
+    sorting2 = sorting2.rename_units(new_unit_ids=[1, 2])
+
+    aggregated_sorting = aggregate_units([sorting1, sorting2])
+    assert aggregated_sorting.get_num_units() == 5
+    assert list(aggregated_sorting.get_unit_ids()) == ["0", "1", "2", "3", "4"]
+
+
 if __name__ == "__main__":
     test_unitsaggregationsorting()
diff --git a/src/spikeinterface/core/unitsaggregationsorting.py b/src/spikeinterface/core/unitsaggregationsorting.py
index ea019268fb..9eb37e31ea 100644
--- a/src/spikeinterface/core/unitsaggregationsorting.py
+++ b/src/spikeinterface/core/unitsaggregationsorting.py
@@ -34,7 +34,21 @@ def __init__(self, sorting_list, renamed_unit_ids=None):
             )
             unit_ids = list(renamed_unit_ids)
         else:
-            unit_ids = list(np.arange(num_all_units))
+            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])
+                all_units_ids_are_unique = np.unique(combined_ids).size == num_all_units
+
+            if all_ids_are_same_type and all_units_ids_are_unique:
+                unit_ids = combined_ids
+            else:
+                default_unit_ids = [str(i) for i in range(num_all_units)]
+                if all_ids_are_same_type and np.issubdtype(unit_ids_dtypes[0], np.integer):
+                    unit_ids = np.arange(num_all_units, dtype=np.uint64)
+                else:
+                    unit_ids = default_unit_ids
 
         # unit map maps unit ids that are used to get spike trains
         u_id = 0