diff --git a/arkindex/dataimport/migrations/0002_repository_revision.py b/arkindex/dataimport/migrations/0002_repository_revision.py
index 93169f0c49328f5e214ceb0472fcebf75001ab3d..e97c33f85bb45d43abf2e99cc6f2d6674cb886f9 100644
--- a/arkindex/dataimport/migrations/0002_repository_revision.py
+++ b/arkindex/dataimport/migrations/0002_repository_revision.py
@@ -82,7 +82,7 @@ class Migration(migrations.Migration):
             name='watched_branches',
             field=arkindex.project.fields.ArrayField(
                 base_field=models.CharField(max_length=50),
-                default=['refs/heads/master'],
+                default=arkindex.dataimport.models.repository_default_branches,
                 size=None,
             ),
         ),
diff --git a/arkindex/dataimport/models.py b/arkindex/dataimport/models.py
index 500a52ad5a42d3392fa44c058daba05aab205dab..799d18347291e4f66a7a4fe82c59cc47f5c45aed 100644
--- a/arkindex/dataimport/models.py
+++ b/arkindex/dataimport/models.py
@@ -146,6 +146,15 @@ class RepositorySource(Enum):
     GitLab = 'gitlab'
 
 
+def repository_default_branches():
+    '''
+    This is needed to avoid re-using the same list instance
+    as Repository.watched_branches default on new instances
+    See Django warning postgres.E003
+    '''
+    return list('refs/heads/master')
+
+
 class Repository(models.Model):
     id = models.UUIDField(primary_key=True, default=uuid.uuid4)
     url = models.URLField(unique=True)
@@ -154,7 +163,7 @@ class Repository(models.Model):
     clone_token = models.CharField(max_length=250)
     corpus = models.ForeignKey('documents.Corpus', on_delete=models.CASCADE, related_name='repos')
     user = models.ForeignKey('users.User', on_delete=models.CASCADE, related_name='repos')
-    watched_branches = ArrayField(models.CharField(max_length=50), default=['refs/heads/master'])
+    watched_branches = ArrayField(models.CharField(max_length=50), default=repository_default_branches)
 
     class Meta:
         verbose_name_plural = 'repositories'
diff --git a/requirements.txt b/requirements.txt
index 6e67d2223c12169996f7e0c4d0d1fc7210e3ec39..47f9c1391f4c1d99f96573df956b5afea930a1ff 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,7 +2,7 @@ celery==4.2.0
 celery_once==2.0.0
 certifi==2017.7.27.1
 chardet==3.0.4
-Django==2.0
+Django==2.1
 django-enumfields==0.10.0
 djangorestframework==3.7.1
 django-webpack-loader==0.5.0