diff --git a/webinterface.py b/webinterface.py
index f3f184ae..96de328b 100644
--- a/webinterface.py
+++ b/webinterface.py
@@ -2748,7 +2748,7 @@ def weekDayOfMonthStart(monthNumber: int,year: int) -> int:
     """Gets the day number of the first day of the month
     1=sun, 7=sat
     """
-    firstDayOfMonth=datetime(year, monthNumber, 1, 0, 0)
+    firstDayOfMonth=datetime.datetime(year, monthNumber, 1, 0, 0)
     return int(firstDayOfMonth.strftime("%w"))+1
 
 def htmlCalendar(translate: {}, \