diff --git a/aiohttp/client.py b/aiohttp/client.py
index 343d20436e..94f2d129ca 100644
--- a/aiohttp/client.py
+++ b/aiohttp/client.py
@@ -294,7 +294,7 @@ def __init__(
         # We initialise _connector to None immediately, as it's referenced in __del__()
         # and could cause issues if an exception occurs during initialisation.
         self._connector: Optional[BaseConnector] = None
-        if base_url is None or isinstance(base_url, URL):
+        if base_url is None or type(base_url) is URL:
             self._base_url: Optional[URL] = base_url
             self._base_url_origin = None if base_url is None else base_url.origin()
         else:
diff --git a/aiohttp/client_reqrep.py b/aiohttp/client_reqrep.py
index 602d6da5f9..4bf0292c1d 100644
--- a/aiohttp/client_reqrep.py
+++ b/aiohttp/client_reqrep.py
@@ -234,8 +234,9 @@ def __init__(
                 f"Method cannot contain non-token characters {method!r} "
                 f"(found at least {match.group()!r})"
             )
-        assert isinstance(url, URL), url
-        assert isinstance(proxy, (URL, type(None))), proxy
+        assert type(url) is URL, url
+        if proxy is not None:
+            assert type(proxy) is URL, proxy
         # FIXME: session is None in tests only, need to fix tests
         # assert session is not None
         self._session = cast("ClientSession", session)
@@ -795,7 +796,7 @@ def __init__(
         loop: asyncio.AbstractEventLoop,
         session: "ClientSession",
     ) -> None:
-        assert isinstance(url, URL)
+        assert type(url) is URL
         super().__init__()
 
         self.method = method
diff --git a/aiohttp/cookiejar.py b/aiohttp/cookiejar.py
index 85fd7716b5..bf576c698f 100644
--- a/aiohttp/cookiejar.py
+++ b/aiohttp/cookiejar.py
@@ -102,7 +102,7 @@ def __init__(
         self._quote_cookie = quote_cookie
         if treat_as_secure_origin is None:
             self._treat_as_secure_origin: FrozenSet[URL] = frozenset()
-        elif isinstance(treat_as_secure_origin, URL):
+        elif type(treat_as_secure_origin) is URL:
             self._treat_as_secure_origin = frozenset({treat_as_secure_origin.origin()})
         elif isinstance(treat_as_secure_origin, str):
             self._treat_as_secure_origin = frozenset(
@@ -301,7 +301,7 @@ def update_cookies(self, cookies: LooseCookies, response_url: URL = URL()) -> No
 
     def filter_cookies(self, request_url: URL) -> "BaseCookie[str]":
         """Returns this jar's cookies filtered by their attributes."""
-        if not isinstance(request_url, URL):
+        if type(request_url) is not URL:
             warnings.warn(
                 "The method accepts yarl.URL instances only, got {}".format(
                     type(request_url)
diff --git a/aiohttp/helpers.py b/aiohttp/helpers.py
index 895ab5cfc3..642f359d20 100644
--- a/aiohttp/helpers.py
+++ b/aiohttp/helpers.py
@@ -160,7 +160,7 @@ def decode(cls, auth_header: str, encoding: str = "latin1") -> "BasicAuth":
     @classmethod
     def from_url(cls, url: URL, *, encoding: str = "latin1") -> Optional["BasicAuth"]:
         """Create BasicAuth from url."""
-        if not isinstance(url, URL):
+        if type(url) is not URL:
             raise TypeError("url should be yarl.URL instance")
         # Check raw_user and raw_password first as yarl is likely
         # to already have these values parsed from the netloc in the cache.