diff --git a/app/models/writing_conference.rb b/app/models/writing_conference.rb
index 18ce8af..d10e1f3 100644
--- a/app/models/writing_conference.rb
+++ b/app/models/writing_conference.rb
@@ -96,7 +96,7 @@ class WritingConference
         same_year = period_start_ym[0] == period_end_ym[0]
         same_month = period_start_ym[1] == period_end_ym[1]
         if same_year && same_month
-          date = self.period_start_date.strftime(date_format.sub('%d', "%d-#{self.period_end_date.day}"))
+          date = self.period_start_date.strftime(date_format.sub('%d', "%d-#{self.period_end_date.strftime('%d')}"))
         elsif same_year
           month_date_format = date_format.match(/(%m|%d)[\-\/\.]*(%m|%d)/)[0] rescue ''
           date = self.period_start_date.strftime(date_format.sub(month_date_format, "#{month_date_format}-#{self.period_end_date.strftime(month_date_format)}"))