diff --git a/rowers/views.py b/rowers/views.py
index 3cda06e0..beb6ecd0 100644
--- a/rowers/views.py
+++ b/rowers/views.py
@@ -2437,7 +2437,7 @@ def histo(request,theuser=0,
 	deltaform = DeltaDaysForm(request.POST)
 	if deltaform.is_valid():
 	    deltadays = deltaform.cleaned_data['deltadays']
-	    if deltadays != 0:
+	    if deltadays != 0 and deltadays != None:
 		enddate = timezone.now()
 		startdate = enddate-datetime.timedelta(days=deltadays)
 		if startdate > enddate: