diff --git a/aioresponses/core.py b/aioresponses/core.py
index 2aa8e05..566e678 100644
--- a/aioresponses/core.py
+++ b/aioresponses/core.py
@@ -29,6 +29,7 @@
 )
 from aiohttp.helpers import TimerNoop
 from multidict import CIMultiDict, CIMultiDictProxy
+from packaging.version import Version
 
 from .compat import (
     URL,
@@ -36,10 +37,9 @@
     stream_reader_factory,
     merge_params,
     normalize_url,
-    RequestInfo,
+    RequestInfo, AIOHTTP_VERSION,
 )
 
-
 _FuncT = TypeVar("_FuncT", bound=Callable[..., Any])
 
 
@@ -223,7 +223,7 @@ def __repr__(self) -> str:
 class aioresponses(object):
     """Mock aiohttp requests made by ClientSession."""
     _matches = None  # type: Dict[str, RequestMatch]
-    _responses = None  # type: List[ClientResponse]
+    _responses: List[ClientResponse] = None
     requests = None  # type: Dict
 
     def __init__(self, **kwargs: Any):
@@ -500,13 +500,15 @@ async def _request_mock(self, orig_self: ClientSession,
         if orig_self.closed:
             raise RuntimeError('Session is closed')
 
-        # Join url with ClientSession._base_url
-        url = orig_self._build_url(url)
-        url_origin = str(url)
-
-        # Combine ClientSession headers with passed headers
-        if orig_self.headers:
-            kwargs["headers"] = orig_self._prepare_headers(kwargs.get("headers"))
+        if AIOHTTP_VERSION >= Version('3.8.0'):
+            # Join url with ClientSession._base_url
+            url = orig_self._build_url(url)
+            url_origin = str(url)
+            # Combine ClientSession headers with passed headers
+            if orig_self.headers:
+                kwargs["headers"] = orig_self._prepare_headers(kwargs.get("headers"))
+        else:
+            url_origin = url
 
         url = normalize_url(merge_params(url, kwargs.get('params')))
         url_str = str(url)
diff --git a/requirements-dev.txt b/requirements-dev.txt
index bb31c52..04cea66 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,6 +1,6 @@
 pip
 wheel
-flake8==3.8.3
+flake8==5.0.4
 tox==3.19.0
 coverage==5.2.1
 Sphinx==1.5.6
@@ -10,5 +10,4 @@ pytest-html==2.1.1
 ddt==1.4.1
 typing
 asynctest==0.13.0
-yarl==1.9.4
-setuptools==69.5.1
+yarl==1.9.4
\ No newline at end of file
diff --git a/setup.cfg b/setup.cfg
index 0b0fe1d..9db058d 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -35,6 +35,7 @@ universal = 1
 
 [flake8]
 exclude = docs
+max-line-length = 120
 
 [tool:pytest]
 testpaths = tests
diff --git a/tests/test_aioresponses.py b/tests/test_aioresponses.py
index 23fce89..7b53b0b 100644
--- a/tests/test_aioresponses.py
+++ b/tests/test_aioresponses.py
@@ -86,6 +86,7 @@ async def test_returned_instance_and_status_code(self, m):
         ("http://example.com/", "/api?foo=bar#fragment")
     )
     @aioresponses()
+    @skipIf(condition=AIOHTTP_VERSION < Version('3.8.0'), reason='aiohttp must be >= 3.8.0')
     async def test_base_url(self, base_url, relative_url, m):
         m.get(self.url, status=200)
         self.session = ClientSession(base_url=base_url)
@@ -93,6 +94,7 @@ async def test_base_url(self, base_url, relative_url, m):
         self.assertEqual(response.status, 200)
 
     @aioresponses()
+    @skipIf(condition=AIOHTTP_VERSION < Version('3.8.0'), reason='aiohttp must be >= 3.8.0')
     async def test_session_headers(self, m):
         m.get(self.url)
         self.session = ClientSession(headers={"Authorization": "Bearer foobar"})