diff --git a/media/migrations/0043_auto_20211023_2012.py b/media/migrations/0043_auto_20211023_2012.py
index a1bc2f1..618dba3 100644
--- a/media/migrations/0043_auto_20211023_2012.py
+++ b/media/migrations/0043_auto_20211023_2012.py
@@ -21,6 +21,7 @@ class Migration(migrations.Migration):
             name='Borrowable',
             fields=[
                 ('id', models.AutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('isbn', media.fields.ISBNField(blank=True, help_text='You may be able to scan it from a bar code.', max_length=28, null=True, unique=True, validators=[media.validators.isbn_validator], verbose_name='ISBN')),
                 ('title', models.CharField(max_length=255, verbose_name='title')),
                 ('present', models.BooleanField(default=False, help_text='Tell that the medium is present in the Mediatek.', verbose_name='present')),
                 ('polymorphic_ctype', models.ForeignKey(editable=False, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='polymorphic_media.borrowable_set+', to='contenttypes.ContentType')),
@@ -74,7 +75,6 @@ class Migration(migrations.Migration):
             name='Book',
             fields=[
                 ('medium_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='media.Medium')),
-                ('isbn', media.fields.ISBNField(blank=True, help_text='You may be able to scan it from a bar code.', max_length=28, null=True, unique=True, validators=[media.validators.isbn_validator], verbose_name='ISBN')),
                 ('subtitle', models.CharField(blank=True, max_length=255, verbose_name='subtitle')),
                 ('number_of_pages', models.PositiveIntegerField(blank=True, null=True, verbose_name='number of pages')),
                 ('publish_date', models.DateField(blank=True, null=True, verbose_name='publish date')),
diff --git a/media/models.py b/media/models.py
index e16c65d..0932058 100644
--- a/media/models.py
+++ b/media/models.py
@@ -32,6 +32,14 @@ class Author(models.Model):
 
 
 class Borrowable(PolymorphicModel):
+    isbn = ISBNField(
+        _('ISBN'),
+        help_text=_('You may be able to scan it from a bar code.'),
+        unique=True,
+        blank=True,
+        null=True,
+    )
+
     title = models.CharField(
         max_length=255,
         verbose_name=_("title"),
@@ -83,14 +91,6 @@ class Medium(Borrowable):
 
 
 class Book(Medium):
-    isbn = ISBNField(
-        _('ISBN'),
-        help_text=_('You may be able to scan it from a bar code.'),
-        unique=True,
-        blank=True,
-        null=True,
-    )
-
     subtitle = models.CharField(
         verbose_name=_('subtitle'),
         max_length=255,