diff --git a/matemat/util/monthdelta.py b/matemat/util/monthdelta.py
index 78cbd28..b93e2ab 100644
--- a/matemat/util/monthdelta.py
+++ b/matemat/util/monthdelta.py
@@ -21,9 +21,12 @@ def add_months(d: datetime, months: int) -> datetime:
     # Iterate the months between the passed date and the target month
     for i in range(months):
         days += calendar.monthrange(*nextmonth)[1]
-        nextmonth = calendar.nextmonth(*nextmonth)
+        if nextmonth[1] == 12:
+            nextmonth = nextmonth[0] + 1, 1
+        else:
+            nextmonth = nextmonth[0], nextmonth[1] + 1
     # Set the day of month temporarily to 1, then add the day offset to reach the 1st of the target month
     newdate: datetime = d.replace(day=1) + timedelta(days=days)
     # Re-set the day of month to the intended value, but capped by the max. day in the target month
-    newdate = newdate.replace(day=min(d.day, calendar.monthlen(newdate.year, newdate.month)))
+    newdate = newdate.replace(day=min(d.day, calendar.monthrange(newdate.year, newdate.month)[1]))
     return newdate