diff --git a/sqlalchemy_utils/types/weekdays.py b/sqlalchemy_utils/types/weekdays.py
index e3c3e95..5a3635c 100644
--- a/sqlalchemy_utils/types/weekdays.py
+++ b/sqlalchemy_utils/types/weekdays.py
@@ -66,10 +66,12 @@ class WeekDaysType(types.TypeDecorator, ScalarCoercible):
 
     def process_bind_param(self, value, dialect):
         if isinstance(value, WeekDays):
-            return value.as_bit_string()
+            value = value.as_bit_string()
 
-        if isinstance(value, six.string_types):
-            return value
+        if dialect.name == 'mysql':
+            func = bytes if six.PY3 else bytearray
+            return func(value, 'utf8')
+        return value
 
     def process_result_value(self, value, dialect):
         if value is not None:
diff --git a/tests/types/test_weekdays.py b/tests/types/test_weekdays.py
index 1bda6f2..682b616 100644
--- a/tests/types/test_weekdays.py
+++ b/tests/types/test_weekdays.py
@@ -35,7 +35,7 @@ class WeekDaysTypeTestCase(TestCase):
         assert isinstance(schedule.working_days, WeekDays)
 
     def test_scalar_attributes_get_coerced_to_objects(self):
-        schedule = self.Schedule(working_days=u'1010101')
+        schedule = self.Schedule(working_days='1010101')
 
         assert isinstance(schedule.working_days, WeekDays)