diff --git a/model_clone/__init__.py b/model_clone/__init__.py
index a8dee106..cdcbbb49 100644
--- a/model_clone/__init__.py
+++ b/model_clone/__init__.py
@@ -4,5 +4,11 @@
 
 from model_clone.admin import CloneModelAdmin, CloneModelAdminMixin
 from model_clone.mixins.clone import CloneMixin
+from model_clone.utils import create_copy_of_instance
 
-__all__ = ["CloneMixin", "CloneModelAdmin", "CloneModelAdminMixin"]
+__all__ = [
+    "CloneMixin",
+    "CloneModelAdmin",
+    "CloneModelAdminMixin",
+    "create_copy_of_instance",
+]
diff --git a/model_clone/tests/__init__.py b/model_clone/tests/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/model_clone/tests.py b/model_clone/tests/test_clone_mixin.py
similarity index 100%
rename from model_clone/tests.py
rename to model_clone/tests/test_clone_mixin.py
diff --git a/model_clone/tests/test_create_copy_of_instance.py b/model_clone/tests/test_create_copy_of_instance.py
new file mode 100644
index 00000000..df98ccbc
--- /dev/null
+++ b/model_clone/tests/test_create_copy_of_instance.py
@@ -0,0 +1,42 @@
+from django.contrib.auth import get_user_model
+from django.core.exceptions import ValidationError
+from django.db import IntegrityError
+from django.test import TestCase
+from django.utils.text import slugify
+
+from model_clone import create_copy_of_instance
+from sample.models import Library, Book
+
+User = get_user_model()
+
+
+class CreateCopyOfInstanceTestCase(TestCase):
+    @classmethod
+    def setUpTestData(cls):
+        cls.user1 = User.objects.create(username="user 1")
+        cls.user2 = User.objects.create(username="user 2")
+
+    def test_cloning_model_with_custom_id(self):
+        instance = Library.objects.create(name="First library", user=self.user1)
+        clone = create_copy_of_instance(instance, attrs={"user": self.user2})
+
+        self.assertNotEqual(instance.pk, clone.pk)
+        self.assertEqual(clone.user, self.user2)
+
+    def test_cloning_unique_fk_field_without_a_fallback_value_is_invalid(self):
+        name = "New Library"
+        instance = Library.objects.create(name=name, user=self.user1)
+
+        with self.assertRaises(ValidationError):
+            create_copy_of_instance(instance)
+
+    def test_cloning_excluded_field_without_a_fallback_value_is_invalid(self):
+        name = "New Library"
+        instance = Book.objects.create(
+            name=name, created_by=self.user1, slug=slugify(name)
+        )
+
+        with self.assertRaises(IntegrityError):
+            create_copy_of_instance(
+                instance, exclude={"slug"}, attrs={"created_by": self.user2}
+            )
diff --git a/model_clone/utils.py b/model_clone/utils.py
index 1713f0d9..5500c985 100644
--- a/model_clone/utils.py
+++ b/model_clone/utils.py
@@ -11,28 +11,30 @@ def create_copy_of_instance(instance, exclude=(), save_new=True, attrs=None):
     """
     Clone an instance of `django.db.models.Model`.
 
-    Args:
-        instance(django.db.models.Model): The model instance to clone.
-        exclude(list|set): List or set of fields to exclude from unique validation.
-        save_new(bool): Save the model instance after duplication calling .save().
-        attrs(dict): Kwargs of field and value to set on the duplicated instance.
-
-    Returns:
-        (django.db.models.Model): The new duplicated instance.
-
-    Examples:
-        >>> from django.contrib.auth import get_user_model
-        >>> from sample.models import Book
-        >>> instance = Book.objects.create(name='The Beautiful Life')
-        >>> instance.pk
-        1
-        >>> instance.name
-        "The Beautiful Life"
-        >>> duplicate = instance.make_clone(attrs={'name': 'Duplicate Book 2'})
-        >>> duplicate.pk
-        2
-        >>> duplicate.name
-        "Duplicate Book 2"
+    :param instance: The model instance to clone.
+    :type instance: django.db.models.Model
+    :param exclude: List or set of fields to exclude from unique validation.
+    :type exclude: list|set
+    :param save_new: Save the model instance after duplication calling .save().
+    :type save_new: bool
+    :param attrs: Kwargs of field and value to set on the duplicated instance.
+    :type attrs: dict
+    :return: The new duplicated instance.
+    :rtype: django.db.models.Model
+
+    :example:
+    >>> from django.contrib.auth import get_user_model
+    >>> from sample.models import Book
+    >>> instance = Book.objects.create(name='The Beautiful Life')
+    >>> instance.pk
+    1
+    >>> instance.name
+    "The Beautiful Life"
+    >>> duplicate = instance.make_clone(attrs={'name': 'Duplicate Book 2'})
+    >>> duplicate.pk
+    2
+    >>> duplicate.name
+    "Duplicate Book 2"
     """
 
     defaults = {}
@@ -52,13 +54,17 @@ def create_copy_of_instance(instance, exclude=(), save_new=True, attrs=None):
         if all(
             [
                 not f.auto_created,
+                not f.primary_key,
                 f.concrete,
                 f.editable,
                 f not in instance.__class__._meta.related_objects,
                 f not in instance.__class__._meta.many_to_many,
             ]
         ):
-            defaults[f.attname] = getattr(instance, f.attname, f.get_default())
+            # Prevent duplicates
+            if f.name not in attrs:
+                defaults[f.attname] = getattr(instance, f.attname, f.get_default())
+
     defaults.update(attrs)
 
     new_obj = instance.__class__(**defaults)
@@ -66,7 +72,13 @@ def create_copy_of_instance(instance, exclude=(), save_new=True, attrs=None):
     exclude = exclude or [
         f.name
         for f in instance._meta.fields
-        if any([f.name not in defaults, f.has_default(), f.null])
+        if any(
+            [
+                all([f.name not in defaults, f.attname not in defaults]),
+                f.has_default(),
+                f.null,
+            ]
+        )
     ]
 
     try: