diff --git a/addons/hr_holidays/models/hr_leave.py b/addons/hr_holidays/models/hr_leave.py
index 9be317b69ca..8af111277ce 100644
--- a/addons/hr_holidays/models/hr_leave.py
+++ b/addons/hr_holidays/models/hr_leave.py
@@ -196,8 +196,9 @@ class HolidaysRequest(models.Model):
             date_from = fields.Datetime.from_string(date_from)
             date_to = fields.Datetime.from_string(date_to)
         else:
-            date_from = timezone(self.env.user.tz).localize(datetime.combine(first_day, hour_from)).astimezone(UTC)
-            date_to = timezone(self.env.user.tz).localize(datetime.combine(last_day, hour_to)).astimezone(UTC)
+            tz = self.env.user.tz or 'UTC'
+            date_from = timezone(tz).localize(datetime.combine(first_day, hour_from)).astimezone(UTC)
+            date_to = timezone(tz).localize(datetime.combine(last_day, hour_to)).astimezone(UTC)
 
         self.date_from = date_from
         self.date_to = date_to