diff --git a/consultation_analyser/consultations/migrations/0002_alter_theme_options_theme_question_and_more.py b/consultation_analyser/consultations/migrations/0002_alter_theme_options_theme_question_and_more.py
new file mode 100644
index 000000000..defd03b8f
--- /dev/null
+++ b/consultation_analyser/consultations/migrations/0002_alter_theme_options_theme_question_and_more.py
@@ -0,0 +1,30 @@
+# Generated by Django 5.0.3 on 2024-03-26 21:27
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("consultations", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name="theme",
+            options={},
+        ),
+        migrations.AddField(
+            model_name="theme",
+            name="question",
+            field=models.ForeignKey(
+                null=True, on_delete=django.db.models.deletion.CASCADE, to="consultations.question"
+            ),
+        ),
+        migrations.AddConstraint(
+            model_name="theme",
+            constraint=models.UniqueConstraint(
+                fields=("summary", "label", "keywords", "question"), name="unique_up_to_question"
+            ),
+        ),
+    ]
diff --git a/consultation_analyser/consultations/models.py b/consultation_analyser/consultations/models.py
index a841308e3..10cf31110 100644
--- a/consultation_analyser/consultations/models.py
+++ b/consultation_analyser/consultations/models.py
@@ -61,6 +61,12 @@ class Theme(UUIDPrimaryKeyModel, TimeStampedModel):
     label = models.CharField(max_length=256, blank=True)
     summary = models.TextField(blank=True)
     keywords = models.JSONField(default=list)
+    question = models.ForeignKey(Question, on_delete=models.CASCADE, null=True)
+
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(fields=["summary", "label", "keywords", "question"], name="unique_up_to_question"),
+        ]
 
 
 class Answer(UUIDPrimaryKeyModel, TimeStampedModel):
diff --git a/docs/erd.png b/docs/erd.png
index 51b60ed8a..1703189a2 100644
Binary files a/docs/erd.png and b/docs/erd.png differ