diff --git a/calendar/teachingdates/templates/iso.tex.j2 b/calendar/teachingdates/templates/iso.tex.j2
index b2b7166..c98886a 100644
--- a/calendar/teachingdates/templates/iso.tex.j2
+++ b/calendar/teachingdates/templates/iso.tex.j2
@@ -1,5 +1,4 @@
 % ISO-8601 calendar weeks for \VAR{year}.
-\BLOCK{for week, date in data.items()}
-\BLOCK{set eow = date|eow(end_of_week)}
-\newcommand{ISOWeek\VAR{week|num2words}}{\VAR{date.isoformat()}--\VAR{eow.isoformat()}}
+\BLOCK{for week, date in weeks.items()}
+\newcommand{ISOWeek\VAR{week|num2words}}{\VAR{date.isoformat()}--\VAR{(date + eow_offset).isoformat()}}
 \BLOCK{endfor}