diff --git a/src/spikeinterface/postprocessing/tests/test_valid_unit_periods.py b/src/spikeinterface/postprocessing/tests/test_valid_unit_periods.py
index 6d34264eac..3ba057d059 100644
--- a/src/spikeinterface/postprocessing/tests/test_valid_unit_periods.py
+++ b/src/spikeinterface/postprocessing/tests/test_valid_unit_periods.py
@@ -34,8 +34,8 @@ def test_user_defined_periods(self):
                 periods[idx]["unit_index"] = unit_index
                 period_start = num_samples // 4
                 period_duration = num_samples // 2
-                periods[idx]["start_sample_index"] = period_start
-                periods[idx]["end_sample_index"] = period_start + period_duration
+                periods[idx]["start_sample_index"] = period_start - unit_index * 10
+                periods[idx]["end_sample_index"] = period_start + period_duration + unit_index * 10
                 periods[idx]["segment_index"] = segment_index
 
         sorting_analyzer = self._prepare_sorting_analyzer(
@@ -48,8 +48,17 @@ def test_user_defined_periods(self):
             minimum_valid_period_duration=1,
         )
         # check that valid periods correspond to user defined periods
-        ext_periods = ext.get_data(outputs="numpy")
-        np.testing.assert_array_equal(ext_periods, periods)
+        ext_periods_numpy = ext.get_data(outputs="numpy")
+        np.testing.assert_array_equal(ext_periods_numpy, periods)
+
+        # check that `numpy` and `by_unit` outputs are the same
+        ext_periods_by_unit = ext.get_data(outputs="by_unit")
+        for segment_index in range(num_segments):
+            for unit_index, unit_id in enumerate(unit_ids):
+                periods_numpy_seg0 = ext_periods_numpy[ext_periods_numpy["segment_index"] == segment_index]
+                periods_numpy_unit = periods_numpy_seg0[periods_numpy_seg0["unit_index"] == unit_index]
+                period = [(periods_numpy_unit["start_sample_index"][0], periods_numpy_unit["end_sample_index"][0])]
+                assert period == ext_periods_by_unit[segment_index][unit_id]
 
     def test_user_defined_periods_as_arrays(self):
         unit_ids = self.sorting.unit_ids
diff --git a/src/spikeinterface/postprocessing/valid_unit_periods.py b/src/spikeinterface/postprocessing/valid_unit_periods.py
index 020396e38d..a76cd703aa 100644
--- a/src/spikeinterface/postprocessing/valid_unit_periods.py
+++ b/src/spikeinterface/postprocessing/valid_unit_periods.py
@@ -548,12 +548,12 @@ def _get_data(self, outputs: str = "by_unit"):
             for segment_index in range(self.sorting_analyzer.get_num_segments()):
                 segment_mask = good_periods_array["segment_index"] == segment_index
                 periods_dict = {}
-                for unit_index in unit_ids:
-                    periods_dict[unit_index] = []
+                for unit_index, unit_id in enumerate(unit_ids):
+                    periods_dict[unit_id] = []
                     unit_mask = good_periods_array["unit_index"] == unit_index
                     good_periods_unit_segment = good_periods_array[segment_mask & unit_mask]
                     for start, end in good_periods_unit_segment[["start_sample_index", "end_sample_index"]]:
-                        periods_dict[unit_index].append((start, end))
+                        periods_dict[unit_id].append((start, end))
                 good_periods.append(periods_dict)
 
         return good_periods