diff --git a/chord_metadata_service/chord/ingest/phenopackets.py b/chord_metadata_service/chord/ingest/phenopackets.py
index 6bc1c85c2..56d557d80 100644
--- a/chord_metadata_service/chord/ingest/phenopackets.py
+++ b/chord_metadata_service/chord/ingest/phenopackets.py
@@ -315,7 +315,7 @@ def get_or_create_interpretation_diagnosis(
     interpretation_id = interpretation.get("id")
     diag_obj, created = pm.Diagnosis.objects.get_or_create(
         id=interpretation_id,
-        disease=diagnosis.get("disease", {}),
+        disease=diagnosis["disease"],
         extra_properties=remove_computed_properties(diagnosis.get("extra_properties", {})),
     )
 
diff --git a/chord_metadata_service/phenopackets/migrations/0017_alter_diagnosis_disease.py b/chord_metadata_service/phenopackets/migrations/0017_alter_diagnosis_disease.py
new file mode 100644
index 000000000..71359380a
--- /dev/null
+++ b/chord_metadata_service/phenopackets/migrations/0017_alter_diagnosis_disease.py
@@ -0,0 +1,19 @@
+# Generated by Django 5.2.10 on 2026-01-16 20:11
+
+import chord_metadata_service.restapi.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('phenopackets', '0016_biosample_fts_extra_phenopacket_fts_extra'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='diagnosis',
+            name='disease',
+            field=models.JSONField(validators=[chord_metadata_service.restapi.validators.JsonSchemaValidator(formats=None, schema_ref='ONTOLOGY_CLASS')]),
+        ),
+    ]
diff --git a/chord_metadata_service/phenopackets/models.py b/chord_metadata_service/phenopackets/models.py
index 168d47425..4afd3201c 100644
--- a/chord_metadata_service/phenopackets/models.py
+++ b/chord_metadata_service/phenopackets/models.py
@@ -470,7 +470,7 @@ class Diagnosis(BaseTimeStamp, ToFTSReprMixin):
     """
     id = models.CharField(primary_key=True, max_length=200,
                           help_text="Unique ID, uses the parent Interpretation's id when ingesting.")
-    disease = models.JSONField(null=True, blank=True, validators=[ontology_validator])
+    disease = models.JSONField(validators=[ontology_validator])
     genomic_interpretations = models.ManyToManyField(
         GenomicInterpretation, blank=True,
         help_text='The genomic elements assessed as being responsible for the disease.')