--- a/cubicweb/web/views/calendar.py	Tue Dec 17 21:21:55 2019 +0100
+++ b/cubicweb/web/views/calendar.py	Thu Dec 19 08:13:22 2019 +0100
@@ -101,8 +101,8 @@
                     elt.add(stop_kw).value = ical_task.stop
 
             buff = ical.serialize()
-            if not isinstance(buff, unicode):
-                buff = unicode(buff, self._cw.encoding)
+            if not isinstance(buff, str):
+                buff = str(buff, self._cw.encoding)
             self.w(buff)
 
 except ImportError: