diff --git a/biscuit/apps/chronos/models.py b/biscuit/apps/chronos/models.py
index 436c27d82ea10bb92fc9821b3098dffffe1e53d6..3842b5e46246a9426de74dde13dd8060e8863bce 100644
--- a/biscuit/apps/chronos/models.py
+++ b/biscuit/apps/chronos/models.py
@@ -83,7 +83,7 @@ class LessonPeriod(models.Model):
     room = models.ForeignKey('Room', models.CASCADE, null=True)
 
     substitution = models.OneToOneField('LessonSubstitution', models.CASCADE,
-                                        'lesson_period', null=True)
+                                        related_name='lesson_period', null=True)
 
     def get_subject(self):
         if self.substitution: