diff --git a/src/utils/gcal-date-time-utils.c b/src/utils/gcal-date-time-utils.c
index 733e4109..658bf6fd 100644
--- a/src/utils/gcal-date-time-utils.c
+++ b/src/utils/gcal-date-time-utils.c
@@ -84,7 +84,7 @@ gcal_date_time_get_start_of_week (GDateTime *date)
 
   first_weekday = get_first_weekday ();
   weekday = g_date_time_get_day_of_week (date) % 7;
-  n_days_after_week_start = (weekday - first_weekday) % 7;
+  n_days_after_week_start = (7 + weekday - first_weekday) % 7;
 
   start_of_week = g_date_time_add_days (date, -n_days_after_week_start);