diff --git a/holoviews/plotting/mpl/chart.py b/holoviews/plotting/mpl/chart.py
index 03e5750ed6..58782852c0 100644
--- a/holoviews/plotting/mpl/chart.py
+++ b/holoviews/plotting/mpl/chart.py
@@ -333,8 +333,8 @@ def initialize_plot(self, ranges=None):
 
         # Get plot ranges and values
         dims = hist.dimensions()[:2]
-        edges, hvals, widths, lims, isdatetime = self._process_hist(hist)
-        if isdatetime and not dims[0].value_format:
+        edges, hvals, widths, lims, is_datetime = self._process_hist(hist)
+        if is_datetime and not dims[0].value_format:
             dt_format = Dimension.type_formatters[np.datetime64]
             dims[0] = dims[0](value_format=DateFormatter(dt_format))
 
@@ -381,14 +381,13 @@ def _process_hist(self, hist):
         hist_vals = np.array(values)
         xlim = hist.range(0)
         ylim = hist.range(1)
-        isdatetime = False
-        if isdatetime(edges):
+        is_datetime = isdatetime(edges)
+        if is_datetime:
             edges = np.array([dt64_to_dt(e) if isinstance(e, np.datetime64) else e for e in edges])
             edges = date2num(edges)
             xlim = tuple(dt_to_int(v, 'D') for v in xlim)
-            isdatetime = True
         widths = np.diff(edges)
-        return edges[:-1], hist_vals, widths, xlim+ylim, isdatetime
+        return edges[:-1], hist_vals, widths, xlim+ylim, is_datetime
 
 
     def _compute_ticks(self, element, edges, widths, lims):