diff --git a/pendulum/pendulum.py b/pendulum/pendulum.py
index 19f6b460..8ec1ec9a 100644
--- a/pendulum/pendulum.py
+++ b/pendulum/pendulum.py
@@ -769,6 +769,8 @@ def set_week_starts_at(cls, value):
 
         :type value: int
         """
+        if value not in cls._days:
+            raise ValueError('Invalid day of the week: {}'.format(value))
         cls._week_starts_at = value
 
     @classmethod
@@ -787,6 +789,8 @@ def set_week_ends_at(cls, value):
 
         :type value: int
         """
+        if value not in cls._days:
+            raise ValueError('Invalid day of the week: {}'.format(value))
         cls._week_ends_at = value
 
     @classmethod
@@ -799,13 +803,17 @@ def get_weekend_days(cls):
         return cls._weekend_days
 
     @classmethod
-    def set_weekend_days(cls, value):
+    def set_weekend_days(cls, values):
         """
         Set weekend days.
 
         :type value: list
         """
-        cls._weekend_days = value
+        for value in values:
+            if value not in cls._days:
+                raise ValueError('Invalid day of the week: {}'
+                                 .format(value))
+        cls._weekend_days = values
 
     # Normalization Rule
     @classmethod
diff --git a/tests/pendulum_tests/test_day_of_week_modifiers.py b/tests/pendulum_tests/test_day_of_week_modifiers.py
index 627bed84..ebd1b664 100644
--- a/tests/pendulum_tests/test_day_of_week_modifiers.py
+++ b/tests/pendulum_tests/test_day_of_week_modifiers.py
@@ -9,6 +9,9 @@
 
 class DayOfWeekModifiersTest(AbstractTestCase):
 
+    def test_set_weekend_days_invalid_value(self):
+        self.assertRaises(ValueError, Pendulum.set_weekend_days, [7])
+
     def test_get_weekend_days(self):
         self.assertEqual(
             [pendulum.SATURDAY, pendulum.SUNDAY],
@@ -21,11 +24,17 @@ def test_get_weekend_days(self):
         )
         Pendulum.set_weekend_days([pendulum.SATURDAY, pendulum.SUNDAY])
 
+    def test_set_week_ends_at_invalid_value(self):
+        self.assertRaises(ValueError, Pendulum.set_week_ends_at, 7)
+
     def test_get_week_ends_at(self):
         Pendulum.set_week_ends_at(pendulum.SATURDAY)
         self.assertEqual(Pendulum.get_week_ends_at(), pendulum.SATURDAY)
         Pendulum.set_week_ends_at(pendulum.SUNDAY)
 
+    def test_set_week_starts_at_invalid_value(self):
+        self.assertRaises(ValueError, Pendulum.set_week_starts_at, 7)
+
     def test_get_week_starts_at(self):
         Pendulum.set_week_starts_at(pendulum.TUESDAY)
         self.assertEqual(Pendulum.get_week_starts_at(), pendulum.TUESDAY)