diff --git a/superset/viz.py b/superset/viz.py
index a97b04e985014..8bb65824d1a5b 100644
--- a/superset/viz.py
+++ b/superset/viz.py
@@ -173,8 +173,10 @@ def query_obj(self):
 
         self.time_shift = utils.parse_human_timedelta(time_shift)
 
-        from_dttm = utils.parse_human_datetime(since) - self.time_shift
-        to_dttm = utils.parse_human_datetime(until) - self.time_shift
+        since = utils.parse_human_datetime(since)
+        until = utils.parse_human_datetime(until)
+        from_dttm = None if since is None else (since - self.time_shift)
+        to_dttm = None if until is None else (until - self.time_shift)
         if from_dttm and to_dttm and from_dttm > to_dttm:
             raise Exception(_('From date cannot be larger than to date'))