diff --git a/src/spikeinterface/widgets/unit_waveforms_density_map.py b/src/spikeinterface/widgets/unit_waveforms_density_map.py
index 9543cbf734..627e6c2af9 100644
--- a/src/spikeinterface/widgets/unit_waveforms_density_map.py
+++ b/src/spikeinterface/widgets/unit_waveforms_density_map.py
@@ -83,8 +83,8 @@ def __init__(
         templates = ext_templates.get_templates(unit_ids=unit_ids)
         bin_min = np.min(templates) * 1.3
         bin_max = np.max(templates) * 1.3
-        bin_size = (bin_max - bin_min) / 100
-        bins = np.arange(bin_min, bin_max, bin_size)
+        num_bins = 100
+        bins = np.linspace(bin_min, bin_max, num_bins + 1)
 
         # 2d histograms
         if same_axis:
@@ -121,14 +121,9 @@ def __init__(
                 wfs = wfs_
 
             # make histogram density
-            wfs_flat = wfs.swapaxes(1, 2).reshape(wfs.shape[0], -1)
-            hist2d = np.zeros((wfs_flat.shape[1], bins.size))
-            indexes0 = np.arange(wfs_flat.shape[1])
-
-            wf_bined = np.floor((wfs_flat - bin_min) / bin_size).astype("int32")
-            wf_bined = wf_bined.clip(0, bins.size - 1)
-            for d in wf_bined:
-                hist2d[indexes0, d] += 1
+            wfs_flat = wfs.swapaxes(1, 2).reshape(wfs.shape[0], -1)  # num_spikes x times*num_channels
+            hists_per_timepoint = [np.histogram(one_timepoint, bins=bins)[0] for one_timepoint in wfs_flat.T]
+            hist2d = np.stack(hists_per_timepoint)
 
             if same_axis:
                 if all_hist2d is None:
@@ -169,7 +164,6 @@ def __init__(
         BaseWidget.__init__(self, plot_data, backend=backend, **backend_kwargs)
 
     def plot_matplotlib(self, data_plot, **backend_kwargs):
-        import matplotlib.pyplot as plt
         from .utils_matplotlib import make_mpl_figure
 
         dp = to_attr(data_plot)