diff --git a/tests/migrations/0003_i49product_i49veterinary_alter_accesskey_id_and_more.py b/tests/migrations/0003_i49product_i49veterinary_alter_accesskey_id_and_more.py
new file mode 100644
index 0000000..4426be2
--- /dev/null
+++ b/tests/migrations/0003_i49product_i49veterinary_alter_accesskey_id_and_more.py
@@ -0,0 +1,239 @@
+# Generated by Django 4.2.6 on 2023-10-31 17:11
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("tests", "0002_alter_profile_sites_setnullforeignkey_and_more"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="I49Product",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("number", models.CharField(max_length=50)),
+                ("cost", models.FloatField()),
+            ],
+        ),
+        migrations.CreateModel(
+            name="I49Veterinary",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("name", models.CharField(max_length=50)),
+            ],
+        ),
+        migrations.AlterField(
+            model_name="accesskey",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="anotheravatar",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="anotherprofile",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="avatar",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="custompk",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="document",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="foreignkeychild",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="foreignkeyparent",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="i86genre",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="i86name",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="manytomanychild",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="manytomanyparent",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="onetoonechild",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="onetooneparent",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="page",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="profile",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="site",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="tag",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="taggeditem",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="team",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="ufmchild",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="ufmparent",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.AlterField(
+            model_name="user",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+        migrations.CreateModel(
+            name="I49ProductDetail",
+            fields=[
+                (
+                    "id",
+                    models.BigAutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("cost", models.FloatField()),
+                (
+                    "product",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE,
+                        related_name="product_details",
+                        to="tests.i49product",
+                    ),
+                ),
+                (
+                    "veterinary",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.PROTECT,
+                        to="tests.i49veterinary",
+                    ),
+                ),
+            ],
+            options={
+                "unique_together": {("product", "veterinary")},
+            },
+        ),
+    ]
diff --git a/tests/models.py b/tests/models.py
index df28c1e..0ee41fc 100644
--- a/tests/models.py
+++ b/tests/models.py
@@ -168,3 +168,20 @@ class I86Name(models.Model):
 class I86Genre(models.Model):
     pass
 
+
+class I49Veterinary(models.Model):
+    name = models.CharField(max_length=50)
+
+class I49Product(models.Model):
+    number = models.CharField(max_length=50)
+    cost = models.FloatField()
+
+
+class I49ProductDetail(models.Model):
+    product = models.ForeignKey("I49Product", on_delete=models.CASCADE, related_name='product_details')
+    veterinary = models.ForeignKey("I49Veterinary", on_delete=models.PROTECT)
+    cost = models.FloatField()
+
+    class Meta:
+        unique_together = ('product', 'veterinary')
+ 
\ No newline at end of file
diff --git a/tests/serializers.py b/tests/serializers.py
index 811e035..4bbbbdf 100644
--- a/tests/serializers.py
+++ b/tests/serializers.py
@@ -2,6 +2,7 @@
 from rest_framework import serializers
 from rest_framework.exceptions import ValidationError
 from rest_framework.validators import UniqueValidator
+from rest_framework.relations import PrimaryKeyRelatedField
 
 from drf_writable_nested.serializers import WritableNestedModelSerializer
 from drf_writable_nested.mixins import UniqueFieldsMixin
@@ -374,3 +375,21 @@ class I86GenreSerializer(WritableNestedModelSerializer):
     class Meta:
         model = models.I86Genre
         fields = ('id', 'names',)
+
+
+
+class I49ProductDetailSerializer(serializers.ModelSerializer):
+    id = serializers.IntegerField(required=False)
+    veterinary = PrimaryKeyRelatedField(queryset=models.I49Veterinary.objects)
+
+    class Meta:
+        model = models.I49ProductDetail
+        fields = ('id', 'veterinary', 'cost')
+
+
+class I49ProductSerializerWithPK(WritableNestedModelSerializer):
+    product_details = I49ProductDetailSerializer(many=True)
+
+    class Meta:
+        model = models.I49Product
+        fields = ('id', 'number', 'cost', 'product_details')
diff --git a/tests/test_unique_fields_mixin.py b/tests/test_unique_fields_mixin.py
index 4a036aa..4f3c6f9 100644
--- a/tests/test_unique_fields_mixin.py
+++ b/tests/test_unique_fields_mixin.py
@@ -88,16 +88,46 @@ def test_create_update_failed(self):
         with self.assertRaises(ValidationError) as ctx:
             serializer.save()
         self.assertEqual(
-            ctx.exception.detail,
-            {'child': {'field': [unique_message_error_detail]}}
+            ctx.exception.detail, {"child": {"field": [unique_message_error_detail]}}
         )
 
     def test_unique_field_not_required_for_partial_updates(self):
-        child = models.UFMChild.objects.create(field='value')
+        child = models.UFMChild.objects.create(field="value")
         serializer = serializers.UFMChildSerializer(
-            instance=child,
-            data={},
-            partial=True
+            instance=child, data={}, partial=True
         )
         self.assertTrue(serializer.is_valid())
         serializer.save()
+
+
+class I49Test(TestCase):
+    def test_issue_49(self):
+        veterinary = models.I49Veterinary.objects.create(name="Veterinary 1")
+        serializer = serializers.I49ProductSerializerWithPK(
+            data={
+                "number": "Product XX",
+                "cost": 20000,
+                "product_details": [{"veterinary": veterinary.id, "cost": 10000}],
+            }
+        )
+
+        self.assertTrue(serializer.is_valid())
+        instance = serializer.save()
+
+        assert len(models.I49Product.objects.all()) == 1
+        assert len(models.I49ProductDetail.objects.all()) == 1
+
+        serializer = serializers.I49ProductSerializerWithPK(
+            instance=instance,
+            data={
+                "number": "Product XX",
+                "cost": 20000,
+                "product_details": [{"veterinary": veterinary.id, "cost": 10000}],
+            },
+        )
+
+        self.assertTrue(serializer.is_valid())
+        serializer.save()
+
+        assert len(models.I49Product.objects.all()) == 1
+        assert len(models.I49ProductDetail.objects.all()) == 1