diff --git a/src/gcal-enums.h b/src/gcal-enums.h
index df256330..5634543c 100644
--- a/src/gcal-enums.h
+++ b/src/gcal-enums.h
@@ -51,13 +51,13 @@ typedef enum
 typedef enum
 {
   GCAL_WEEK_DAY_INVALID   = 0,
-  GCAL_WEEK_DAY_SUNDAY    = 1 << 0,
-  GCAL_WEEK_DAY_MONDAY    = 1 << 1,
-  GCAL_WEEK_DAY_TUESDAY   = 1 << 2,
-  GCAL_WEEK_DAY_WEDNESDAY = 1 << 3,
-  GCAL_WEEK_DAY_THURSDAY  = 1 << 4,
-  GCAL_WEEK_DAY_FRIDAY    = 1 << 5,
-  GCAL_WEEK_DAY_SATURDAY  = 1 << 6
+  GCAL_WEEK_DAY_MONDAY    = 1 << 0,
+  GCAL_WEEK_DAY_TUESDAY   = 1 << 1,
+  GCAL_WEEK_DAY_WEDNESDAY = 1 << 2,
+  GCAL_WEEK_DAY_THURSDAY  = 1 << 3,
+  GCAL_WEEK_DAY_FRIDAY    = 1 << 4,
+  GCAL_WEEK_DAY_SATURDAY  = 1 << 5,
+  GCAL_WEEK_DAY_SUNDAY    = 1 << 6
 } GcalWeekDay;
 
 typedef enum
diff --git a/src/gui/common/gcal-date-chooser-day.c b/src/gui/common/gcal-date-chooser-day.c
index ab278607..29f81980 100644
--- a/src/gui/common/gcal-date-chooser-day.c
+++ b/src/gui/common/gcal-date-chooser-day.c
@@ -199,7 +199,7 @@ gcal_date_chooser_day_set_date (GcalDateChooserDay *self,
 
   now = g_date_time_new_now (g_date_time_get_timezone (date));
   today = gcal_date_time_compare_date (date, now) == 0;
-  weekday = g_date_time_get_day_of_week (date) % GCAL_N_WEEKDAYS;
+  weekday = g_date_time_get_day_of_week (date);
 
   if (G_UNLIKELY (today))
     gtk_widget_add_css_class (widget, "today");
diff --git a/src/utils/gcal-utils.c b/src/utils/gcal-utils.c
index 64a68aab..48b59650 100644
--- a/src/utils/gcal-utils.c
+++ b/src/utils/gcal-utils.c
@@ -549,7 +549,7 @@ struct
 
 /**
  * gcal_util_is_workday:
- * @day: a guint representing the day of a week (0…Sunday, 6…Saturday)
+ * @day: a guint representing the ISO 8601 day of a week (1…Monday, 7…Sunday)
  *
  * Checks whether @day is workday or not based on the Territory part of Locale.
  *
@@ -563,7 +563,7 @@ gcal_util_is_workday (guint day)
   gchar territory[3] = { 0, };
   guint i;
 
-  if (day > GCAL_N_WEEKDAYS - 1)
+  if (day < 1 || day > GCAL_N_WEEKDAYS)
     return FALSE;
 
   no_work_days = GCAL_WEEK_DAY_SATURDAY | GCAL_WEEK_DAY_SUNDAY;