diff --git a/welco/qualif/migrations/0001_initial.py b/welco/qualif/migrations/0001_initial.py
index 89f8b96..0606fdd 100644
--- a/welco/qualif/migrations/0001_initial.py
+++ b/welco/qualif/migrations/0001_initial.py
@@ -56,7 +56,7 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='association',
             name='source_type',
-            field=models.ForeignKey(to='contenttypes.ContentType'),
+            field=models.ForeignKey(to='contenttypes.ContentType', on_delete=models.CASCADE),
             preserve_default=True,
         ),
     ]
diff --git a/welco/qualif/models.py b/welco/qualif/models.py
index 8c563f1..a949611 100644
--- a/welco/qualif/models.py
+++ b/welco/qualif/models.py
@@ -24,7 +24,7 @@ from welco.utils import get_wcs_formdef_details, push_wcs_formdata, get_wcs_serv
 
 
 class Association(models.Model):
-    source_type = models.ForeignKey(ContentType)
+    source_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
     source_pk = models.PositiveIntegerField()
     source = GenericForeignKey('source_type', 'source_pk')
     comments = models.TextField(blank=True, verbose_name=_('Comments'))