diff --git a/src/spikeinterface/curation/curation_tools.py b/src/spikeinterface/curation/curation_tools.py
index ff2c32d07f..281a623161 100644
--- a/src/spikeinterface/curation/curation_tools.py
+++ b/src/spikeinterface/curation/curation_tools.py
@@ -104,35 +104,35 @@ def _find_duplicated_spikes_random(spike_train: np.ndarray, censored_period: int
 
     @numba.jit(nopython=True, nogil=True, cache=False)
     def _find_duplicated_spikes_keep_first_iterative(spike_train, censored_period):
-        indices_of_duplicates = numba.typed.List()
         N = len(spike_train)
+        is_duplicate = np.zeros(N, dtype=np.bool_)
 
         for i in range(N - 1):
-            if i in indices_of_duplicates:
+            if is_duplicate[i]:
                 continue
 
             for j in range(i + 1, N):
                 if spike_train[j] - spike_train[i] > censored_period:
                     break
-                indices_of_duplicates.append(j)
+                is_duplicate[j] = True
 
-        return np.asarray(indices_of_duplicates)
+        return np.nonzero(is_duplicate)[0]
 
-    @numba.jit(nopython=True, nogil=True, cache=True)
+    @numba.jit(nopython=True, nogil=True, cache=False)
     def _find_duplicated_spikes_keep_last_iterative(spike_train, censored_period):
-        indices_of_duplicates = numba.typed.List()
         N = len(spike_train)
+        is_duplicate = np.zeros(N, dtype=np.bool_)
 
         for i in range(N - 1, 0, -1):
-            if i in indices_of_duplicates:
+            if is_duplicate[i]:
                 continue
 
             for j in range(i - 1, -1, -1):
                 if spike_train[i] - spike_train[j] > censored_period:
                     break
-                indices_of_duplicates.append(j)
+                is_duplicate[j] = True
 
-        return np.asarray(indices_of_duplicates)
+        return np.nonzero(is_duplicate)[0]
 
 
 def find_duplicated_spikes(