diff --git a/django_mongodb_backend/fields/array.py b/django_mongodb_backend/fields/array.py
index 49c9e6ad..e21afdcf 100644
--- a/django_mongodb_backend/fields/array.py
+++ b/django_mongodb_backend/fields/array.py
@@ -1,6 +1,5 @@
 import json
 
-from django.contrib.postgres.validators import ArrayMaxLengthValidator
 from django.core import checks, exceptions
 from django.db.models import DecimalField, Field, Func, IntegerField, Transform, Value
 from django.db.models.fields.mixins import CheckFieldDefaultMixin
@@ -10,6 +9,7 @@
 from ..forms import SimpleArrayField
 from ..query_utils import process_lhs, process_rhs
 from ..utils import prefix_validation_error
+from ..validators import ArrayMaxLengthValidator, LengthValidator
 
 __all__ = ["ArrayField"]
 
@@ -27,13 +27,19 @@ class ArrayField(CheckFieldDefaultMixin, Field):
     }
     _default_hint = ("list", "[]")
 
-    def __init__(self, base_field, size=None, **kwargs):
+    def __init__(self, base_field, max_size=None, size=None, **kwargs):
         self.base_field = base_field
+        self.max_size = max_size
         self.size = size
+        if self.max_size:
+            self.default_validators = [
+                *self.default_validators,
+                ArrayMaxLengthValidator(self.max_size),
+            ]
         if self.size:
             self.default_validators = [
                 *self.default_validators,
-                ArrayMaxLengthValidator(self.size),
+                LengthValidator(self.size),
             ]
         # For performance, only add a from_db_value() method if the base field
         # implements it.
@@ -98,6 +104,14 @@ def check(self, **kwargs):
                             id="django_mongodb_backend.array.W004",
                         )
                     )
+        if self.size and self.max_size:
+            errors.append(
+                checks.Error(
+                    "ArrayField cannot specify both size and max_size.",
+                    obj=self,
+                    id="django_mongodb_backend.array.E003",
+                )
+            )
         return errors
 
     def set_attributes_from_name(self, name):
@@ -124,12 +138,11 @@ def deconstruct(self):
         name, path, args, kwargs = super().deconstruct()
         if path == "django_mongodb_backend.fields.array.ArrayField":
             path = "django_mongodb_backend.fields.ArrayField"
-        kwargs.update(
-            {
-                "base_field": self.base_field.clone(),
-                "size": self.size,
-            }
-        )
+        kwargs["base_field"] = self.base_field.clone()
+        if self.max_size is not None:
+            kwargs["max_size"] = self.max_size
+        if self.size is not None:
+            kwargs["size"] = self.size
         return name, path, args, kwargs
 
     def to_python(self, value):
@@ -213,7 +226,8 @@ def formfield(self, **kwargs):
             **{
                 "form_class": SimpleArrayField,
                 "base_field": self.base_field.formfield(),
-                "max_length": self.size,
+                "max_length": self.max_size,
+                "length": self.size,
                 **kwargs,
             }
         )
diff --git a/django_mongodb_backend/forms/fields/array.py b/django_mongodb_backend/forms/fields/array.py
index 0de48dff..854508cc 100644
--- a/django_mongodb_backend/forms/fields/array.py
+++ b/django_mongodb_backend/forms/fields/array.py
@@ -2,11 +2,11 @@
 from itertools import chain
 
 from django import forms
-from django.core.exceptions import ValidationError
+from django.core.exceptions import ImproperlyConfigured, ValidationError
 from django.utils.translation import gettext_lazy as _
 
 from ...utils import prefix_validation_error
-from ...validators import ArrayMaxLengthValidator, ArrayMinLengthValidator
+from ...validators import ArrayMaxLengthValidator, ArrayMinLengthValidator, LengthValidator
 
 
 class SimpleArrayField(forms.CharField):
@@ -14,16 +14,26 @@ class SimpleArrayField(forms.CharField):
         "item_invalid": _("Item %(nth)s in the array did not validate:"),
     }
 
-    def __init__(self, base_field, *, delimiter=",", max_length=None, min_length=None, **kwargs):
+    def __init__(
+        self, base_field, *, delimiter=",", max_length=None, min_length=None, length=None, **kwargs
+    ):
         self.base_field = base_field
         self.delimiter = delimiter
         super().__init__(**kwargs)
+        if (min_length is not None or max_length is not None) and length is not None:
+            invalid_param = "max_length" if max_length is not None else "min_length"
+            raise ImproperlyConfigured(
+                f"The length and {invalid_param} parameters are mutually exclusive."
+            )
         if min_length is not None:
             self.min_length = min_length
             self.validators.append(ArrayMinLengthValidator(int(min_length)))
         if max_length is not None:
             self.max_length = max_length
             self.validators.append(ArrayMaxLengthValidator(int(max_length)))
+        if length is not None:
+            self.length = length
+            self.validators.append(LengthValidator(int(length)))
 
     def clean(self, value):
         value = super().clean(value)
diff --git a/django_mongodb_backend/validators.py b/django_mongodb_backend/validators.py
index 6005152e..5ca6cbe2 100644
--- a/django_mongodb_backend/validators.py
+++ b/django_mongodb_backend/validators.py
@@ -1,4 +1,5 @@
-from django.core.validators import MaxLengthValidator, MinLengthValidator
+from django.core.validators import BaseValidator, MaxLengthValidator, MinLengthValidator
+from django.utils.deconstruct import deconstructible
 from django.utils.translation import ngettext_lazy
 
 
@@ -16,3 +17,19 @@ class ArrayMinLengthValidator(MinLengthValidator):
         "List contains %(show_value)d items, it should contain no fewer than %(limit_value)d.",
         "show_value",
     )
+
+
+@deconstructible
+class LengthValidator(BaseValidator):
+    message = ngettext_lazy(
+        "List contains %(show_value)d item, it should contain %(limit_value)d.",
+        "List contains %(show_value)d items, it should contain %(limit_value)d.",
+        "show_value",
+    )
+    code = "length"
+
+    def compare(self, a, b):
+        return a != b
+
+    def clean(self, x):
+        return len(x)
diff --git a/docs/source/ref/forms.rst b/docs/source/ref/forms.rst
index 64c42755..934af20e 100644
--- a/docs/source/ref/forms.rst
+++ b/docs/source/ref/forms.rst
@@ -33,7 +33,7 @@ Stores an :class:`~bson.objectid.ObjectId`.
 ``SimpleArrayField``
 --------------------
 
-.. class:: SimpleArrayField(base_field, delimiter=',', max_length=None, min_length=None)
+.. class:: SimpleArrayField(base_field, delimiter=',', length=None, max_length=None, min_length=None)
 
     A field which maps to an array. It is represented by an HTML ``<input>``.
 
@@ -91,6 +91,14 @@ Stores an :class:`~bson.objectid.ObjectId`.
             in cases where the delimiter is a valid character in the underlying
             field. The delimiter does not need to be only one character.
 
+    .. attribute:: length
+
+        This is an optional argument which validates that the array contains
+        the stated number of items.
+
+        ``length`` may not be specified along with ``max_length`` or
+        ``min_length``.
+
     .. attribute:: max_length
 
         This is an optional argument which validates that the array does not
diff --git a/docs/source/ref/models/fields.rst b/docs/source/ref/models/fields.rst
index 83bd4848..47a3149c 100644
--- a/docs/source/ref/models/fields.rst
+++ b/docs/source/ref/models/fields.rst
@@ -8,13 +8,12 @@ Some MongoDB-specific fields are available in ``django_mongodb_backend.fields``.
 ``ArrayField``
 --------------
 
-.. class:: ArrayField(base_field, size=None, **options)
+.. class:: ArrayField(base_field, max_size=None, size=None, **options)
 
     A field for storing lists of data. Most field types can be used, and you
-    pass another field instance as the :attr:`base_field
-    <ArrayField.base_field>`. You may also specify a :attr:`size
-    <ArrayField.size>`. ``ArrayField`` can be nested to store multi-dimensional
-    arrays.
+    pass another field instance as the :attr:`~ArrayField.base_field`. You may
+    also specify a :attr:`~ArrayField.size` or :attr:`~ArrayField.max_size`.
+    ``ArrayField`` can be nested to store multi-dimensional arrays.
 
     If you give the field a :attr:`~django.db.models.Field.default`, ensure
     it's a callable such as ``list`` (for an empty default) or a callable that
@@ -59,12 +58,21 @@ Some MongoDB-specific fields are available in ``django_mongodb_backend.fields``.
         of data and configuration, and serialization are all delegated to the
         underlying base field.
 
-    .. attribute:: size
+    .. attribute:: max_size
 
         This is an optional argument.
 
         If passed, the array will have a maximum size as specified, validated
-        only by forms.
+        by forms and model validation, but not enforced by the database.
+
+        The ``max_size`` and ``size`` options are mutually exclusive.
+
+    .. attribute:: size
+
+        This is an optional argument.
+
+        If passed, the array will have size as specified, validated by forms
+        and model validation, but not enforced by the database.
 
 Querying ``ArrayField``
 ~~~~~~~~~~~~~~~~~~~~~~~
@@ -168,8 +176,8 @@ Index transforms
 ^^^^^^^^^^^^^^^^
 
 Index transforms index into the array. Any non-negative integer can be used.
-There are no errors if it exceeds the :attr:`size <ArrayField.size>` of the
-array. The lookups available after the transform are those from the
+There are no errors if it exceeds the :attr:`max_size <ArrayField.max_size>` of
+the array. The lookups available after the transform are those from the
 :attr:`base_field <ArrayField.base_field>`. For example:
 
 .. code-block:: pycon
diff --git a/docs/source/releases/5.1.x.rst b/docs/source/releases/5.1.x.rst
index 02c2019d..2e36e6d8 100644
--- a/docs/source/releases/5.1.x.rst
+++ b/docs/source/releases/5.1.x.rst
@@ -7,6 +7,10 @@ Django MongoDB Backend 5.1.x
 
 *Unreleased*
 
+- Backward-incompatible: :class:`~django_mongodb_backend.fields.ArrayField`\'s
+  :attr:`~.ArrayField.size` parameter is renamed to
+  :attr:`~.ArrayField.max_size`. The :attr:`~.ArrayField.size` parameter is now
+  used to enforce fixed-length arrays.
 - Added support for :doc:`database caching </topics/cache>`.
 - Fixed ``QuerySet.raw_aggregate()`` field initialization when the document key
   order doesn't match the order of the model's fields.
diff --git a/tests/forms_tests_/test_array.py b/tests/forms_tests_/test_array.py
index 58ab5566..360a68c4 100644
--- a/tests/forms_tests_/test_array.py
+++ b/tests/forms_tests_/test_array.py
@@ -21,21 +21,15 @@ def test_valid(self):
 
     def test_to_python_fail(self):
         field = SimpleArrayField(forms.IntegerField())
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "Item 1 in the array did not validate: Enter a whole number."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean("a,b,9")
-        self.assertEqual(
-            cm.exception.messages[0],
-            "Item 1 in the array did not validate: Enter a whole number.",
-        )
 
     def test_validate_fail(self):
         field = SimpleArrayField(forms.CharField(required=True))
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "Item 3 in the array did not validate: This field is required."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean("a,b,")
-        self.assertEqual(
-            cm.exception.messages[0],
-            "Item 3 in the array did not validate: This field is required.",
-        )
 
     def test_validate_fail_base_field_error_params(self):
         field = SimpleArrayField(forms.CharField(max_length=2))
@@ -68,12 +62,9 @@ def test_validate_fail_base_field_error_params(self):
 
     def test_validators_fail(self):
         field = SimpleArrayField(forms.RegexField("[a-e]{2}"))
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "Item 1 in the array did not validate: Enter a valid value."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean("a,bc,de")
-        self.assertEqual(
-            cm.exception.messages[0],
-            "Item 1 in the array did not validate: Enter a valid value.",
-        )
 
     def test_delimiter(self):
         field = SimpleArrayField(forms.CharField(), delimiter="|")
@@ -92,21 +83,15 @@ def test_prepare_value(self):
 
     def test_max_length(self):
         field = SimpleArrayField(forms.CharField(), max_length=2)
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "List contains 3 items, it should contain no more than 2."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean("a,b,c")
-        self.assertEqual(
-            cm.exception.messages[0],
-            "List contains 3 items, it should contain no more than 2.",
-        )
 
     def test_min_length(self):
         field = SimpleArrayField(forms.CharField(), min_length=4)
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "List contains 3 items, it should contain no fewer than 4."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean("a,b,c")
-        self.assertEqual(
-            cm.exception.messages[0],
-            "List contains 3 items, it should contain no fewer than 4.",
-        )
 
     def test_min_length_singular(self):
         field = SimpleArrayField(forms.IntegerField(), min_length=2)
@@ -115,11 +100,34 @@ def test_min_length_singular(self):
         with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean([1])
 
+    def test_size_length(self):
+        field = SimpleArrayField(forms.CharField(max_length=27), length=4)
+        msg = "List contains 3 items, it should contain 4."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
+            field.clean(["a", "b", "c"])
+        msg = "List contains 5 items, it should contain 4."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
+            field.clean(["a", "b", "c", "d", "e"])
+
+    def test_size_length_singular(self):
+        field = SimpleArrayField(forms.CharField(max_length=27), length=4)
+        msg = "List contains 1 item, it should contain 4."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
+            field.clean(["a"])
+
     def test_required(self):
         field = SimpleArrayField(forms.CharField(), required=True)
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "This field is required."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean("")
-        self.assertEqual(cm.exception.messages[0], "This field is required.")
+
+    def test_length_and_max_min_length(self):
+        msg = "The length and max_length parameters are mutually exclusive."
+        with self.assertRaisesMessage(exceptions.ImproperlyConfigured, msg):
+            SimpleArrayField(forms.CharField(), max_length=3, length=2)
+        msg = "The length and min_length parameters are mutually exclusive."
+        with self.assertRaisesMessage(exceptions.ImproperlyConfigured, msg):
+            SimpleArrayField(forms.CharField(), min_length=3, length=2)
 
     def test_model_field_formfield(self):
         model_field = ArrayField(models.CharField(max_length=27))
@@ -128,11 +136,17 @@ def test_model_field_formfield(self):
         self.assertIsInstance(form_field.base_field, forms.CharField)
         self.assertEqual(form_field.base_field.max_length, 27)
 
+    def test_model_field_formfield_max_size(self):
+        model_field = ArrayField(models.CharField(max_length=27), max_size=4)
+        form_field = model_field.formfield()
+        self.assertIsInstance(form_field, SimpleArrayField)
+        self.assertEqual(form_field.max_length, 4)
+
     def test_model_field_formfield_size(self):
         model_field = ArrayField(models.CharField(max_length=27), size=4)
         form_field = model_field.formfield()
         self.assertIsInstance(form_field, SimpleArrayField)
-        self.assertEqual(form_field.max_length, 4)
+        self.assertEqual(form_field.length, 4)
 
     def test_model_field_choices(self):
         model_field = ArrayField(models.IntegerField(choices=((1, "A"), (2, "B"))))
diff --git a/tests/forms_tests_/test_objectidfield.py b/tests/forms_tests_/test_objectidfield.py
index ee37401b..64a46193 100644
--- a/tests/forms_tests_/test_objectidfield.py
+++ b/tests/forms_tests_/test_objectidfield.py
@@ -23,9 +23,8 @@ def test_clean_empty_string(self):
 
     def test_clean_invalid(self):
         field = ObjectIdField()
-        with self.assertRaises(ValidationError) as cm:
+        with self.assertRaisesMessage(ValidationError, "Enter a valid Object Id."):
             field.clean("invalid")
-        self.assertEqual(cm.exception.messages[0], "Enter a valid Object Id.")
 
     def test_prepare_value(self):
         field = ObjectIdField()
diff --git a/tests/model_fields_/array_default_migrations/0001_initial.py b/tests/model_fields_/array_default_migrations/0001_initial.py
index 4faaed19..0c759c05 100644
--- a/tests/model_fields_/array_default_migrations/0001_initial.py
+++ b/tests/model_fields_/array_default_migrations/0001_initial.py
@@ -21,7 +21,7 @@ class Migration(migrations.Migration):
                 ),
                 (
                     "field",
-                    django_mongodb_backend.fields.ArrayField(models.IntegerField(), size=None),
+                    django_mongodb_backend.fields.ArrayField(models.IntegerField()),
                 ),
             ],
             options={},
diff --git a/tests/model_fields_/array_default_migrations/0002_integerarraymodel_field_2.py b/tests/model_fields_/array_default_migrations/0002_integerarraymodel_field_2.py
index 90f49499..18bfbf99 100644
--- a/tests/model_fields_/array_default_migrations/0002_integerarraymodel_field_2.py
+++ b/tests/model_fields_/array_default_migrations/0002_integerarraymodel_field_2.py
@@ -12,9 +12,7 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name="integerarraydefaultmodel",
             name="field_2",
-            field=django_mongodb_backend.fields.ArrayField(
-                models.IntegerField(), default=[], size=None
-            ),
+            field=django_mongodb_backend.fields.ArrayField(models.IntegerField(), default=[]),
             preserve_default=False,
         ),
     ]
diff --git a/tests/model_fields_/array_index_migrations/0001_initial.py b/tests/model_fields_/array_index_migrations/0001_initial.py
index a32b0529..4113bdd4 100644
--- a/tests/model_fields_/array_index_migrations/0001_initial.py
+++ b/tests/model_fields_/array_index_migrations/0001_initial.py
@@ -22,7 +22,7 @@ class Migration(migrations.Migration):
                 (
                     "char",
                     django_mongodb_backend.fields.ArrayField(
-                        models.CharField(max_length=10), db_index=True, size=100
+                        models.CharField(max_length=10), db_index=True, max_size=100
                     ),
                 ),
                 ("char2", models.CharField(max_length=11, db_index=True)),
diff --git a/tests/model_fields_/test_arrayfield.py b/tests/model_fields_/test_arrayfield.py
index 3b3c4c0c..2b457201 100644
--- a/tests/model_fields_/test_arrayfield.py
+++ b/tests/model_fields_/test_arrayfield.py
@@ -85,15 +85,16 @@ class MyModel(models.Model):
     def test_deconstruct(self):
         field = ArrayField(models.IntegerField())
         name, path, args, kwargs = field.deconstruct()
+        self.assertEqual(kwargs.keys(), {"base_field"})
         new = ArrayField(*args, **kwargs)
         self.assertEqual(type(new.base_field), type(field.base_field))
         self.assertIsNot(new.base_field, field.base_field)
 
-    def test_deconstruct_with_size(self):
-        field = ArrayField(models.IntegerField(), size=3)
+    def test_deconstruct_with_max_size(self):
+        field = ArrayField(models.IntegerField(), max_size=3)
         name, path, args, kwargs = field.deconstruct()
         new = ArrayField(*args, **kwargs)
-        self.assertEqual(new.size, field.size)
+        self.assertEqual(new.max_size, field.max_size)
 
     def test_deconstruct_args(self):
         field = ArrayField(models.CharField(max_length=20))
@@ -645,6 +646,15 @@ class MyModel(models.Model):
         self.assertEqual(len(errors), 1)
         self.assertEqual(errors[0].id, "django_mongodb_backend.array.E002")
 
+    def test_both_size_and_max_size(self):
+        class MyModel(models.Model):
+            field = ArrayField(models.CharField(max_length=3), size=3, max_size=4)
+
+        model = MyModel()
+        errors = model.check()
+        self.assertEqual(len(errors), 1)
+        self.assertEqual(errors[0].id, "django_mongodb_backend.array.E003")
+
     def test_invalid_default(self):
         class MyModel(models.Model):
             field = ArrayField(models.IntegerField(), default=[])
@@ -722,7 +732,7 @@ class MigrationsTests(TransactionTestCase):
     )
     def test_adding_field_with_default(self):
         class IntegerArrayDefaultModel(models.Model):
-            field = ArrayField(models.IntegerField(), size=None)
+            field = ArrayField(models.IntegerField())
 
         table_name = "model_fields__integerarraydefaultmodel"
         self.assertNotIn(table_name, connection.introspection.table_names(None))
@@ -734,8 +744,8 @@ class IntegerArrayDefaultModel(models.Model):
         call_command("migrate", "model_fields_", "0002", verbosity=0)
 
         class UpdatedIntegerArrayDefaultModel(models.Model):
-            field = ArrayField(models.IntegerField(), size=None)
-            field_2 = ArrayField(models.IntegerField(), default=[], size=None)
+            field = ArrayField(models.IntegerField())
+            field_2 = ArrayField(models.IntegerField(), default=[])
 
             class Meta:
                 db_table = "model_fields__integerarraydefaultmodel"
@@ -787,43 +797,51 @@ def test_loading(self):
 class ValidationTests(SimpleTestCase):
     def test_unbounded(self):
         field = ArrayField(models.IntegerField())
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "Item 2 in the array did not validate: This field cannot be null."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg) as cm:
             field.clean([1, None], None)
         self.assertEqual(cm.exception.code, "item_invalid")
-        self.assertEqual(
-            cm.exception.message % cm.exception.params,
-            "Item 2 in the array did not validate: This field cannot be null.",
-        )
 
     def test_blank_true(self):
         field = ArrayField(models.IntegerField(blank=True, null=True))
         # This should not raise a validation error
         field.clean([1, None], None)
 
-    def test_with_size(self):
-        field = ArrayField(models.IntegerField(), size=3)
+    def test_with_max_size(self):
+        field = ArrayField(models.IntegerField(), max_size=3)
         field.clean([1, 2, 3], None)
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "List contains 4 items, it should contain no more than 3."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean([1, 2, 3, 4], None)
-        self.assertEqual(
-            cm.exception.messages[0],
-            "List contains 4 items, it should contain no more than 3.",
-        )
 
-    def test_with_size_singular(self):
-        field = ArrayField(models.IntegerField(), size=1)
+    def test_with_max_size_singular(self):
+        field = ArrayField(models.IntegerField(), max_size=1)
         field.clean([1], None)
         msg = "List contains 2 items, it should contain no more than 1."
         with self.assertRaisesMessage(exceptions.ValidationError, msg):
             field.clean([1, 2], None)
 
+    def test_with_size(self):
+        field = ArrayField(models.IntegerField(), size=3)
+        field.clean([1, 2, 3], None)
+        msg = "List contains 4 items, it should contain 3."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
+            field.clean([1, 2, 3, 4], None)
+
+    def test_with_size_singular(self):
+        field = ArrayField(models.IntegerField(), size=2)
+        field.clean([1, 2], None)
+        msg = "List contains 1 item, it should contain 2."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg):
+            field.clean([1], None)
+
     def test_nested_array_mismatch(self):
         field = ArrayField(ArrayField(models.IntegerField()))
         field.clean([[1, 2], [3, 4]], None)
-        with self.assertRaises(exceptions.ValidationError) as cm:
+        msg = "Nested arrays must have the same length."
+        with self.assertRaisesMessage(exceptions.ValidationError, msg) as cm:
             field.clean([[1, 2], [3, 4, 5]], None)
         self.assertEqual(cm.exception.code, "nested_array_mismatch")
-        self.assertEqual(cm.exception.messages[0], "Nested arrays must have the same length.")
 
     def test_with_base_field_error_params(self):
         field = ArrayField(models.CharField(max_length=2))
diff --git a/tests/model_fields_/test_objectidfield.py b/tests/model_fields_/test_objectidfield.py
index 13356522..b4b00f01 100644
--- a/tests/model_fields_/test_objectidfield.py
+++ b/tests/model_fields_/test_objectidfield.py
@@ -117,12 +117,10 @@ def test_loading(self):
 class ValidationTests(TestCase):
     def test_invalid_objectid(self):
         field = ObjectIdField()
-        with self.assertRaises(ValidationError) as cm:
+        msg = "“550e8400” is not a valid Object Id."
+        with self.assertRaisesMessage(ValidationError, msg) as cm:
             field.clean("550e8400", None)
         self.assertEqual(cm.exception.code, "invalid")
-        self.assertEqual(
-            cm.exception.message % cm.exception.params, "“550e8400” is not a valid Object Id."
-        )
 
     def test_objectid_instance_ok(self):
         value = ObjectId()
diff --git a/tests/validators_/__init__.py b/tests/validators_/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/validators_/tests.py b/tests/validators_/tests.py
new file mode 100644
index 00000000..09a54949
--- /dev/null
+++ b/tests/validators_/tests.py
@@ -0,0 +1,31 @@
+from django.core.exceptions import ValidationError
+from django.test import SimpleTestCase
+
+from django_mongodb_backend.validators import LengthValidator
+
+
+class TestLengthValidator(SimpleTestCase):
+    validator = LengthValidator(10)
+
+    def test_empty(self):
+        msg = "List contains 0 items, it should contain 10."
+        with self.assertRaisesMessage(ValidationError, msg):
+            self.validator([])
+
+    def test_singular(self):
+        msg = "List contains 1 item, it should contain 10."
+        with self.assertRaisesMessage(ValidationError, msg):
+            self.validator([1])
+
+    def test_too_short(self):
+        msg = "List contains 9 items, it should contain 10."
+        with self.assertRaisesMessage(ValidationError, msg):
+            self.validator([1, 2, 3, 4, 5, 6, 7, 8, 9])
+
+    def test_too_long(self):
+        msg = "List contains 11 items, it should contain 10."
+        with self.assertRaisesMessage(ValidationError, msg):
+            self.validator(list(range(11)))
+
+    def test_valid(self):
+        self.assertEqual(self.validator(list(range(10))), None)