diff --git a/expenses_manager/expenses/migrations/0016_alter_transfer_expense_leg_alter_transfer_income_leg.py b/expenses_manager/expenses/migrations/0016_alter_transfer_expense_leg_alter_transfer_income_leg.py
new file mode 100644
index 0000000..353a66f
--- /dev/null
+++ b/expenses_manager/expenses/migrations/0016_alter_transfer_expense_leg_alter_transfer_income_leg.py
@@ -0,0 +1,24 @@
+# Generated by Django 5.2.10 on 2026-09-21 13:35
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('expenses', '0015_link_legacy_transfers'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='transfer',
+            name='expense_leg',
+            field=models.OneToOneField(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='transfer_out', to='expenses.expense'),
+        ),
+        migrations.AlterField(
+            model_name='transfer',
+            name='income_leg',
+            field=models.OneToOneField(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='transfer_in', to='expenses.income'),
+        ),
+    ]
diff --git a/expenses_manager/expenses/models.py b/expenses_manager/expenses/models.py
index 973d859..b6d763b 100644
--- a/expenses_manager/expenses/models.py
+++ b/expenses_manager/expenses/models.py
@@ -356,11 +356,23 @@ class Transfer(models.Model):
     # Las dos patas y la comisión opcional. SET_NULL para que si algo las borra
     # por fuera el Transfer no arrastre, pero el flujo normal las borra en cascada
     # desde el propio Transfer (ver delete()).
+    #
+    # blank=True porque un traspaso siempre acaba con sus dos patas, pero no las
+    # tiene en el instante en que se construye: sync() las crea a partir de él.
+    # Exigirlas en full_clean() describiría mal ese momento.
     expense_leg = models.OneToOneField(
-        Expense, on_delete=models.SET_NULL, null=True, related_name="transfer_out"
+        Expense,
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name="transfer_out",
     )
     income_leg = models.OneToOneField(
-        Income, on_delete=models.SET_NULL, null=True, related_name="transfer_in"
+        Income,
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name="transfer_in",
     )
 
     fee_amount = models.DecimalField(