diff --git a/c2corg_api/search/search_filters.py b/c2corg_api/search/search_filters.py
index 9fbd347b3..d2d544c68 100644
--- a/c2corg_api/search/search_filters.py
+++ b/c2corg_api/search/search_filters.py
@@ -1,7 +1,7 @@
 import logging
 import math
 import re
-from datetime import datetime
+from datetime import datetime, timezone
 from functools import partial
 
 from c2corg_api.models.outing import OUTING_TYPE
@@ -283,7 +283,9 @@ def create_period_filter(field, query_term):
     range_values = [t for t in range_values if t is not None]
 
     def milliseconds_since_first_day_of_year(date):
-        seconds_since_epoch = datetime.strptime(date, '%Y-%m-%d').timestamp()
+        processed_date = datetime.strptime(date, '%Y-%m-%d')
+        # Force UTC, to avoid problems when running on a machine that is not set to UTC
+        seconds_since_epoch = processed_date.replace(tzinfo=timezone.utc).timestamp()
 
         return int(1000 * seconds_since_epoch) % milliseconds_in_one_year