diff -r 80ce81208b08 -r 3051b847c124 server/python/django2/renkanmanager/models.py
--- a/server/python/django2/renkanmanager/models.py	Tue Jun 21 10:30:08 2016 +0200
+++ b/server/python/django2/renkanmanager/models.py	Tue Jun 21 17:53:06 2016 +0200
@@ -133,11 +133,11 @@
             Saves over current revision or saves a new revision entirely.
             Timestamp must be the current revision modification_date.
         """
-        if (not timestamp) or ((self.current_revision is not None) and dateparse.parse_datetime(timestamp) < self.current_revision.modification_date):
+        if (not timestamp) or ((self.current_revision is not None) and timestamp != self.current_revision.modification_date):
             logger.error("SAVING RENKAN: provided timestamp is %r, which isn't current revision modification_date %r", timestamp, self.current_revision.modification_date)
             raise ValidationError(_("Cannot save, provided timestamp is invalid"))
         else:
-            dt_timestamp = dateparse.parse_datetime(timestamp)
+            dt_timestamp = timestamp
 
         if create_new_revision:
             revision_to_update = Revision(parent_renkan=self)