diff --git a/biscuit/apps/chronos/models.py b/biscuit/apps/chronos/models.py
index 9bb1f77ccd3a157f924df5859fac3eebd45135dc..9f65c6ee69b7708cb2a98ed7f8c3e96262cb129c 100644
--- a/biscuit/apps/chronos/models.py
+++ b/biscuit/apps/chronos/models.py
@@ -29,7 +29,7 @@ class TimePeriod(models.Model):
     time_start = models.TimeField(verbose_name=_('Time the period starts'))
     time_end = models.TimeField(verbose_name=_('Time the period ends'))
 
-    def __str__(self): str:
+    def __str__(self) -> str:
         return '%s, %d. period (%s - %s)' % (self.weekday, self.period, self.time_start, self.time_end)
 
     @classmethod