diff --git a/combo_plugin_gnm/templatetags/gnm.py b/combo_plugin_gnm/templatetags/gnm.py
index e9a6dd5..beb3366 100644
--- a/combo_plugin_gnm/templatetags/gnm.py
+++ b/combo_plugin_gnm/templatetags/gnm.py
@@ -124,11 +124,11 @@ def get_time_table_from_specification(specification):
     return (weekday, time_table)
 
 
-def openinghours_to_datetime(codename, hour, minute, base_datetime):
+def openinghours_to_datetime(day_number, hour, minute, base_datetime):
     """
     return the next date and time after base_datetime
     """
-    day_number = EN_ABBREV_WEEKDAYS_LIST.index(codename)
+    day_number = day_number % 7  # ease operations using this parameter
 
     # set next weekday
     days = (7 + day_number - base_datetime.weekday()) % 7
@@ -273,15 +273,15 @@ def get_slots_from_mairie_format(data, base_datetime):
 
         for days_list, time_table in parse_opening_hours_data(data):
             for weekday in days_list:
+                day_number = EN_ABBREV_WEEKDAYS_LIST.index(weekday)
                 start = openinghours_to_datetime(
-                    weekday, int(time_table['start_hour']), int(time_table['start_minute']), base_datetime)
+                    day_number, int(time_table['start_hour']), int(time_table['start_minute']), base_datetime)
                 end = openinghours_to_datetime(
-                    weekday, int(time_table['end_hour']), int(time_table['end_minute']), base_datetime)
+                    day_number, int(time_table['end_hour']), int(time_table['end_minute']), base_datetime)
 
                 # hours may belongs on next day
                 if end < start:
-                    day_number = EN_ABBREV_WEEKDAYS_LIST.index(weekday)
-                    tomorrow = EN_ABBREV_WEEKDAYS_LIST[(day_number + 1) % 7]
+                    tomorrow = day_number + 1
                     end = openinghours_to_datetime(
                         tomorrow, int(time_table['end_hour']), int(time_table['end_minute']), base_datetime)
                     if end < start: