diff --git a/aiohttp_pydantic/injectors.py b/aiohttp_pydantic/injectors.py
index 8594459..a653fd1 100644
--- a/aiohttp_pydantic/injectors.py
+++ b/aiohttp_pydantic/injectors.py
@@ -5,6 +5,8 @@ from typing import Callable, Tuple
 from aiohttp.web_request import BaseRequest
 from pydantic import BaseModel
 
+from .utils import is_pydantic_base_model
+
 
 class AbstractInjector(metaclass=abc.ABCMeta):
     """
@@ -98,7 +100,7 @@ def _parse_func_signature(func: Callable) -> Tuple[dict, dict, dict, dict]:
         if param_spec.kind is param_spec.POSITIONAL_ONLY:
             path_args[param_name] = param_spec.annotation
         elif param_spec.kind is param_spec.POSITIONAL_OR_KEYWORD:
-            if issubclass(param_spec.annotation, BaseModel):
+            if is_pydantic_base_model(param_spec.annotation):
                 body_args[param_name] = param_spec.annotation
             else:
                 qs_args[param_name] = param_spec.annotation
diff --git a/aiohttp_pydantic/oas/view.py b/aiohttp_pydantic/oas/view.py
index 56d2467..b53c167 100644
--- a/aiohttp_pydantic/oas/view.py
+++ b/aiohttp_pydantic/oas/view.py
@@ -3,27 +3,17 @@ from typing import List, Type
 
 from aiohttp.web import Response, json_response
 from aiohttp.web_app import Application
-from pydantic import BaseModel
 
 from aiohttp_pydantic.oas.struct import OpenApiSpec3, OperationObject, PathItem
 
 from ..injectors import _parse_func_signature
+from ..utils import is_pydantic_base_model
 from ..view import PydanticView, is_pydantic_view
 from .typing import is_status_code_type
 
 JSON_SCHEMA_TYPES = {float: "number", str: "string", int: "integer"}
 
 
-def _is_pydantic_base_model(obj):
-    """
-    Return true is obj is a pydantic.BaseModel subclass.
-    """
-    try:
-        return issubclass(obj, BaseModel)
-    except TypeError:
-        return False
-
-
 class _OASResponseBuilder:
     """
     Parse the type annotated as returned by a function and
@@ -35,7 +25,7 @@ class _OASResponseBuilder:
 
     @staticmethod
     def _handle_pydantic_base_model(obj):
-        if _is_pydantic_base_model(obj):
+        if is_pydantic_base_model(obj):
             return obj.schema()
         return {}
 
diff --git a/aiohttp_pydantic/utils.py b/aiohttp_pydantic/utils.py
new file mode 100644
index 0000000..efee749
--- /dev/null
+++ b/aiohttp_pydantic/utils.py
@@ -0,0 +1,11 @@
+from pydantic import BaseModel
+
+
+def is_pydantic_base_model(obj):
+    """
+    Return true is obj is a pydantic.BaseModel subclass.
+    """
+    try:
+        return issubclass(obj, BaseModel)
+    except TypeError:
+        return False
diff --git a/aiohttp_pydantic/view.py b/aiohttp_pydantic/view.py
index e04f71e..a899542 100644
--- a/aiohttp_pydantic/view.py
+++ b/aiohttp_pydantic/view.py
@@ -9,14 +9,8 @@ from aiohttp.web_exceptions import HTTPMethodNotAllowed
 from aiohttp.web_response import StreamResponse
 from pydantic import ValidationError
 
-from .injectors import (
-    AbstractInjector,
-    BodyGetter,
-    HeadersGetter,
-    MatchInfoGetter,
-    QueryGetter,
-    _parse_func_signature,
-)
+from .injectors import (AbstractInjector, BodyGetter, HeadersGetter,
+                        MatchInfoGetter, QueryGetter, _parse_func_signature)
 
 
 class PydanticView(AbstractView):
diff --git a/demo/model.py b/demo/model.py
index a6ef842..5a5b425 100644
--- a/demo/model.py
+++ b/demo/model.py
@@ -4,6 +4,7 @@ from pydantic import BaseModel
 class Pet(BaseModel):
     id: int
     name: str
+    age: int
 
 
 class Error(BaseModel):
diff --git a/demo/view.py b/demo/view.py
index b897f00..bed6260 100644
--- a/demo/view.py
+++ b/demo/view.py
@@ -1,4 +1,4 @@
-from typing import List, Union
+from typing import List, Optional, Union
 
 from aiohttp import web
 
@@ -9,9 +9,11 @@ from .model import Error, Pet
 
 
 class PetCollectionView(PydanticView):
-    async def get(self) -> r200[List[Pet]]:
+    async def get(self, age: Optional[int] = None) -> r200[List[Pet]]:
         pets = self.request.app["model"].list_pets()
-        return web.json_response([pet.dict() for pet in pets])
+        return web.json_response(
+            [pet.dict() for pet in pets if age is None or age == pet.age]
+        )
 
     async def post(self, pet: Pet) -> r201[Pet]:
         self.request.app["model"].add_pet(pet)
diff --git a/tests/test_validation_query_string.py b/tests/test_validation_query_string.py
index 441cf6e..cae7704 100644
--- a/tests/test_validation_query_string.py
+++ b/tests/test_validation_query_string.py
@@ -1,11 +1,13 @@
+from typing import Optional
+
 from aiohttp import web
 
 from aiohttp_pydantic import PydanticView
 
 
 class ArticleView(PydanticView):
-    async def get(self, with_comments: bool):
-        return web.json_response({"with_comments": with_comments})
+    async def get(self, with_comments: bool, age: Optional[int] = None):
+        return web.json_response({"with_comments": with_comments, "age": age})
 
 
 async def test_get_article_without_required_qs_should_return_an_error_message(
@@ -53,7 +55,22 @@ async def test_get_article_with_valid_qs_should_return_the_parsed_type(
     app.router.add_view("/article", ArticleView)
 
     client = await aiohttp_client(app)
+
+    resp = await client.get("/article", params={"with_comments": "yes", "age": 3})
+    assert resp.status == 200
+    assert resp.content_type == "application/json"
+    assert await resp.json() == {"with_comments": True, "age": 3}
+
+
+async def test_get_article_with_valid_qs_and_omitted_optional_should_return_none(
+    aiohttp_client, loop
+):
+    app = web.Application()
+    app.router.add_view("/article", ArticleView)
+
+    client = await aiohttp_client(app)
+
     resp = await client.get("/article", params={"with_comments": "yes"})
     assert resp.status == 200
     assert resp.content_type == "application/json"
-    assert await resp.json() == {"with_comments": True}
+    assert await resp.json() == {"with_comments": True, "age": None}