diff --git a/docs/fields/common-parameters.md b/docs/fields/common-parameters.md
index d5a4c0d..044dfe9 100644
--- a/docs/fields/common-parameters.md
+++ b/docs/fields/common-parameters.md
@@ -158,6 +158,37 @@ Used for data related to given model but not to be stored in the database.
 
 Used in pydantic only.
 
+## overwrite_pydantic_type
+
+By default, ormar uses predefined pydantic field types that it applies on model creation (hence the type hints are optional).
+
+If you want to, you can apply your own type, that will be **completely** replacing the build in one.
+So it's on you as a user to provide a type that is valid in the context of given ormar field type.
+
+!!!warning
+        Note that by default you should use build in arguments that are passed to underlying pydantic field. 
+        
+        You can check what arguments are supported in field types section or in [pydantic](https://pydantic-docs.helpmanual.io/usage/schema/#field-customisation) docs.
+
+!!!danger
+        Setting a wrong type of pydantic field can break your model, so overwrite it only when you know what you are doing.
+        
+        As it's easy to break functionality of ormar the `overwrite_pydantic_type` argument is not available on relation fields!
+
+```python
+# sample overwrites
+class OverwriteTest(ormar.Model):
+    class Meta:
+        tablename = "overwrites"
+        metadata = metadata
+        database = database
+
+    id: int = ormar.Integer(primary_key=True)
+    my_int: str = ormar.Integer(overwrite_pydantic_type=PositiveInt)
+    constraint_dict: Json = ormar.JSON(
+        overwrite_pydantic_type=Optional[Json[Dict[str, int]]])
+```
+
 ## choices
 
 `choices`: `Sequence` = `[]` 
diff --git a/docs/releases.md b/docs/releases.md
index a891e9e..c488d01 100644
--- a/docs/releases.md
+++ b/docs/releases.md
@@ -1,3 +1,10 @@
+# 0.10.17
+
+## ✨ Features
+
+* Allow overwriting the default pydantic type for model fields [#312](https://github.com/collerek/ormar/issues/285)
+* Add support for `sqlalchemy` >=1.4 (requires `databases` >= 0.5.0) [#142](https://github.com/collerek/ormar/issues/142)
+
 # 0.10.16
 
 ## ✨ Features
diff --git a/ormar/__init__.py b/ormar/__init__.py
index 1542801..222d30c 100644
--- a/ormar/__init__.py
+++ b/ormar/__init__.py
@@ -77,7 +77,7 @@ class UndefinedType:  # pragma no cover
 
 Undefined = UndefinedType()
 
-__version__ = "0.10.16"
+__version__ = "0.10.17"
 __all__ = [
     "Integer",
     "BigInteger",
diff --git a/ormar/fields/base.py b/ormar/fields/base.py
index 3310d25..8eb4188 100644
--- a/ormar/fields/base.py
+++ b/ormar/fields/base.py
@@ -31,6 +31,7 @@ class BaseField(FieldInfo):
 
     def __init__(self, **kwargs: Any) -> None:
         self.__type__: type = kwargs.pop("__type__", None)
+        self.__pydantic_type__: type = kwargs.pop("__pydantic_type__", None)
         self.__sample__: type = kwargs.pop("__sample__", None)
         self.related_name = kwargs.pop("related_name", None)
 
diff --git a/ormar/fields/foreign_key.py b/ormar/fields/foreign_key.py
index 707463f..de0774c 100644
--- a/ormar/fields/foreign_key.py
+++ b/ormar/fields/foreign_key.py
@@ -143,12 +143,14 @@ def validate_not_allowed_fields(kwargs: Dict) -> None:
     encrypt_secret = kwargs.pop("encrypt_secret", None)
     encrypt_backend = kwargs.pop("encrypt_backend", None)
     encrypt_custom_backend = kwargs.pop("encrypt_custom_backend", None)
+    overwrite_pydantic_type = kwargs.pop("overwrite_pydantic_type", None)
 
     not_supported = [
         default,
         encrypt_secret,
         encrypt_backend,
         encrypt_custom_backend,
+        overwrite_pydantic_type,
     ]
     if any(x is not None for x in not_supported):
         raise ModelDefinitionError(
diff --git a/ormar/fields/model_fields.py b/ormar/fields/model_fields.py
index f1230b5..8478718 100644
--- a/ormar/fields/model_fields.py
+++ b/ormar/fields/model_fields.py
@@ -84,8 +84,13 @@ class ModelFieldFactory:
         encrypt_backend = kwargs.pop("encrypt_backend", EncryptBackends.NONE)
         encrypt_custom_backend = kwargs.pop("encrypt_custom_backend", None)
 
+        overwrite_pydantic_type = kwargs.pop("overwrite_pydantic_type", None)
+
         namespace = dict(
             __type__=cls._type,
+            __pydantic_type__=overwrite_pydantic_type
+            if overwrite_pydantic_type is not None
+            else cls._type,
             __sample__=cls._sample,
             alias=kwargs.pop("name", None),
             name=None,
diff --git a/ormar/models/helpers/pydantic.py b/ormar/models/helpers/pydantic.py
index 87ed5d1..1423176 100644
--- a/ormar/models/helpers/pydantic.py
+++ b/ormar/models/helpers/pydantic.py
@@ -5,8 +5,8 @@ import pydantic
 from pydantic.fields import ModelField
 from pydantic.utils import lenient_issubclass
 
-from ormar.fields import BaseField  # noqa: I100, I202
-from ormar.exceptions import ModelDefinitionError
+from ormar.exceptions import ModelDefinitionError  # noqa: I100, I202
+from ormar.fields import BaseField
 
 if TYPE_CHECKING:  # pragma no cover
     from ormar import Model
@@ -84,9 +84,15 @@ def populate_pydantic_default_values(attrs: Dict) -> Tuple[Dict, Dict]:
     for field_name, field in potential_fields.items():
         field.name = field_name
         model_fields[field_name] = field
-        attrs["__annotations__"][field_name] = (
+        default_type = (
             field.__type__ if not field.nullable else Optional[field.__type__]
         )
+        overwrite_type = (
+            field.__pydantic_type__
+            if field.__type__ != field.__pydantic_type__
+            else None
+        )
+        attrs["__annotations__"][field_name] = overwrite_type or default_type
     return attrs, model_fields
 
 
diff --git a/ormar/models/model_row.py b/ormar/models/model_row.py
index 3c2dd1c..a9f0680 100644
--- a/ormar/models/model_row.py
+++ b/ormar/models/model_row.py
@@ -10,7 +10,11 @@ from typing import (
     cast,
 )
 
-import sqlalchemy
+try:
+    from sqlalchemy.engine.result import ResultProxy
+except ImportError:  # pragma: no cover
+    from sqlalchemy.engine.result import Row as ResultProxy  # type: ignore
+
 
 from ormar.models import NewBaseModel  # noqa: I202
 from ormar.models.excludable import ExcludableItems
@@ -25,7 +29,7 @@ class ModelRow(NewBaseModel):
     @classmethod
     def from_row(  # noqa: CFQ002
         cls,
-        row: sqlalchemy.engine.ResultProxy,
+        row: ResultProxy,
         source_model: Type["Model"],
         select_related: List = None,
         related_models: Any = None,
@@ -59,7 +63,7 @@ class ModelRow(NewBaseModel):
         :param source_model: model on which relation was defined
         :type source_model: Type[Model]
         :param row: raw result row from the database
-        :type row: sqlalchemy.engine.result.ResultProxy
+        :type row: ResultProxy
         :param select_related: list of names of related models fetched from database
         :type select_related: List
         :param related_models: list or dict of related models
@@ -153,7 +157,7 @@ class ModelRow(NewBaseModel):
     def _populate_nested_models_from_row(  # noqa: CFQ002
         cls,
         item: dict,
-        row: sqlalchemy.engine.ResultProxy,
+        row: ResultProxy,
         source_model: Type["Model"],
         related_models: Any,
         excludable: ExcludableItems,
@@ -183,7 +187,7 @@ class ModelRow(NewBaseModel):
         :param item: dictionary of already populated nested models, otherwise empty dict
         :type item: Dict
         :param row: raw result row from the database
-        :type row: sqlalchemy.engine.result.ResultProxy
+        :type row: ResultProxy
         :param related_models: list or dict of related models
         :type related_models: Union[Dict, List]
         :return: dictionary with keys corresponding to model fields names
@@ -263,7 +267,7 @@ class ModelRow(NewBaseModel):
     @classmethod
     def _populate_through_instance(  # noqa: CFQ002
         cls,
-        row: sqlalchemy.engine.ResultProxy,
+        row: ResultProxy,
         item: Dict,
         related: str,
         excludable: ExcludableItems,
@@ -275,7 +279,7 @@ class ModelRow(NewBaseModel):
         Normally it's child class, unless the query is from queryset.
 
         :param row: row from db result
-        :type row: sqlalchemy.engine.ResultProxy
+        :type row: ResultProxy
         :param item: parent item dict
         :type item: Dict
         :param related: current relation name
@@ -301,7 +305,7 @@ class ModelRow(NewBaseModel):
     @classmethod
     def _create_through_instance(
         cls,
-        row: sqlalchemy.engine.ResultProxy,
+        row: ResultProxy,
         through_name: str,
         related: str,
         excludable: ExcludableItems,
@@ -343,7 +347,7 @@ class ModelRow(NewBaseModel):
     def extract_prefixed_table_columns(
         cls,
         item: dict,
-        row: sqlalchemy.engine.result.ResultProxy,
+        row: ResultProxy,
         table_prefix: str,
         excludable: ExcludableItems,
     ) -> Dict:
diff --git a/requirements.txt b/requirements.txt
index abdd726..696c4aa 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,8 +1,8 @@
-databases[sqlite]>=0.3.2,<=0.4.1
-databases[postgresql]>=0.3.2,<=0.4.1
-databases[mysql]>=0.3.2,<=0.4.1
+databases[sqlite]>=0.3.2,<0.5.1
+databases[postgresql]>=0.3.2,<0.5.1
+databases[mysql]>=0.3.2,<0.5.1
 pydantic >=1.6.1,!=1.7,!=1.7.1,!=1.7.2,!=1.7.3,!=1.8,!=1.8.1,<=1.8.2
-sqlalchemy>=1.3.18,<=1.3.23
+sqlalchemy>=1.3.18,<=1.4.23
 typing_extensions>=3.7,<=3.7.4.3
 orjson
 cryptography
diff --git a/tests/test_model_definition/test_overwriting_pydantic_field_type.py b/tests/test_model_definition/test_overwriting_pydantic_field_type.py
new file mode 100644
index 0000000..0b77592
--- /dev/null
+++ b/tests/test_model_definition/test_overwriting_pydantic_field_type.py
@@ -0,0 +1,54 @@
+from typing import Dict, Optional
+
+import databases
+import pytest
+import sqlalchemy
+from pydantic import Json, PositiveInt, ValidationError
+
+import ormar
+from tests.settings import DATABASE_URL
+
+database = databases.Database(DATABASE_URL, force_rollback=True)
+metadata = sqlalchemy.MetaData()
+
+
+class OverwriteTest(ormar.Model):
+    class Meta:
+        tablename = "overwrites"
+        metadata = metadata
+        database = database
+
+    id: int = ormar.Integer(primary_key=True)
+    my_int: str = ormar.Integer(overwrite_pydantic_type=PositiveInt)
+    constraint_dict: Json = ormar.JSON(
+        overwrite_pydantic_type=Optional[Json[Dict[str, int]]]
+    )
+
+
+@pytest.fixture(autouse=True, scope="module")
+def create_test_database():
+    engine = sqlalchemy.create_engine(DATABASE_URL)
+    metadata.drop_all(engine)
+    metadata.create_all(engine)
+    yield
+    metadata.drop_all(engine)
+
+
+def test_constraints():
+    with pytest.raises(ValidationError) as e:
+        OverwriteTest(my_int=-10)
+    assert "ensure this value is greater than 0" in str(e.value)
+
+    with pytest.raises(ValidationError) as e:
+        OverwriteTest(my_int=10, constraint_dict={"aa": "ab"})
+    assert "value is not a valid integer" in str(e.value)
+
+
+@pytest.mark.asyncio
+async def test_saving():
+    async with database:
+        await OverwriteTest(my_int=5, constraint_dict={"aa": 123}).save()
+
+        test = await OverwriteTest.objects.get()
+        assert test.my_int == 5
+        assert test.constraint_dict == {"aa": 123}