diff --git a/app/models/teaching_period.rb b/app/models/teaching_period.rb
index eaf5d6b2c..e8c0195ac 100644
--- a/app/models/teaching_period.rb
+++ b/app/models/teaching_period.rb
@@ -115,7 +115,10 @@ def date_for_week_and_day(week, day)
 
     start_day_num = start_date.wday
 
-    result = week_start + (day_num - start_day_num).days
+    day_offset = day_num - start_day_num
+    day_offset += 7 if day_offset.negative?
+
+    result = week_start + day_offset.days
 
     for a_break in breaks do
       if result >= a_break.start_date && result < a_break.end_date
diff --git a/test/models/teaching_period_test.rb b/test/models/teaching_period_test.rb
index 863507e2e..e630bb35f 100644
--- a/test/models/teaching_period_test.rb
+++ b/test/models/teaching_period_test.rb
@@ -119,7 +119,7 @@ def test_create_teaching_period_with_invalid_dates
     assert_equal tp.start_date + 3.day + 2.week, tp.date_for_week_and_day(3, 'Thu')
     assert_equal tp.start_date + 4.day + 2.week, tp.date_for_week_and_day(3, 'Fri')
     assert_equal tp.start_date + 5.day, tp.date_for_week_and_day(1, 'Sat')
-    assert_equal tp.start_date - 1.day, tp.date_for_week_and_day(1, 'Sun')
+    assert_equal tp.start_date + 6.days, tp.date_for_week_and_day(1, 'Sun')
   end
 
   test 'can map week and day to date after break' do