diff --git a/src/spikeinterface/comparison/comparisontools.py b/src/spikeinterface/comparison/comparisontools.py
index 3cd856d662..1c3685c666 100644
--- a/src/spikeinterface/comparison/comparisontools.py
+++ b/src/spikeinterface/comparison/comparisontools.py
@@ -188,7 +188,7 @@ def compute_matching_matrix(
         the metrics section in SpikeForest documentation.
         """
 
-        matching_matrix = np.zeros((num_units_train1, num_units_train2), dtype=np.uint16)
+        matching_matrix = np.zeros((num_units_train1, num_units_train2), dtype=np.uint64)
 
         # Used to avoid the same spike matching twice
         last_match_frame1 = -np.ones_like(matching_matrix, dtype=np.int64)
@@ -235,7 +235,7 @@ def compute_matching_matrix(
 def make_match_count_matrix(sorting1, sorting2, delta_frames):
     num_units_sorting1 = sorting1.get_num_units()
     num_units_sorting2 = sorting2.get_num_units()
-    matching_matrix = np.zeros((num_units_sorting1, num_units_sorting2), dtype=np.uint16)
+    matching_matrix = np.zeros((num_units_sorting1, num_units_sorting2), dtype=np.uint64)
 
     spike_vector1_segments = sorting1.to_spike_vector(concatenated=False)
     spike_vector2_segments = sorting2.to_spike_vector(concatenated=False)