diff --git a/combo_plugin_gnm/templatetags/gnm.py b/combo_plugin_gnm/templatetags/gnm.py
index b52cb57..e9aceff 100644
--- a/combo_plugin_gnm/templatetags/gnm.py
+++ b/combo_plugin_gnm/templatetags/gnm.py
@@ -202,7 +202,7 @@ def get_slots_from_mairie_format(data, base_datetime):
             valid_through = parse_datetime(specification.get('validThrough')) if specification.get('validThrough') else next_week
             if not valid_from or not valid_through:
                 continue
-            if 'opens' in specification and 'closes' in specification:
+            if specification.get('opens') and specification.get('closes'):
                 # case when opening periods are defined
                 if base_datetime >= valid_from and base_datetime < valid_through:
                     (opening_time, closing_time, day_number) = get_open_close_from_specification(