Clock freezes seconds after load

After loading the clock app, within a few seconds during which it is responsive, the whole things freezes, and the following is repeatedly written to the app's log:

libecal-CRITICAL **:
               time_days_in_month: assertion 'year >= 1900' failed

I used to have saved Alarms, and I also have saved Event data (from calendar/syncevolution) one or more of which may be causing this problem when the app tries to load them.