diff --git a/src/gen/lib/date.py b/src/gen/lib/date.py
index 1dd3407fc..b364763cb 100644
--- a/src/gen/lib/date.py
+++ b/src/gen/lib/date.py
@@ -624,7 +624,7 @@ class Date:
                 dv[Date._POS_MON] = dv[Date._POS_MON] % 12
         self.dateval = tuple(dv)
         self._calc_sort_value()
-        if day != 0 or dv[Date.POS_DAY] > 28:
+        if day != 0 or dv[Date._POS_DAY] > 28:
             self.set_yr_mon_day(*self.offset(day))
 
     def copy_offset_ymd(self, year=0, month=0, day=0):