diff --git a/CHANGES/8320.bugfix.rst b/CHANGES/8320.bugfix.rst
new file mode 100644
index 00000000000..027074f743b
--- /dev/null
+++ b/CHANGES/8320.bugfix.rst
@@ -0,0 +1 @@
+Fixed the pure python parser to mark a connection as closing when a response has no length -- by :user:`Dreamsorcerer`.
diff --git a/aiohttp/http_parser.py b/aiohttp/http_parser.py
index cce0b788d46..013511917e8 100644
--- a/aiohttp/http_parser.py
+++ b/aiohttp/http_parser.py
@@ -718,7 +718,16 @@ def parse_message(self, lines: List[bytes]) -> RawResponseMessage:
         ) = self.parse_headers(lines)
 
         if close is None:
-            close = version_o <= HttpVersion10
+            if version_o <= HttpVersion10:
+                close = True
+            # https://www.rfc-editor.org/rfc/rfc9112.html#name-message-body-length
+            elif 100 <= status_i < 200 or status_i in {204, 304}:
+                close = False
+            elif hdrs.CONTENT_LENGTH in headers or hdrs.TRANSFER_ENCODING in headers:
+                close = False
+            else:
+                # https://www.rfc-editor.org/rfc/rfc9112.html#section-6.3-2.8
+                close = True
 
         return RawResponseMessage(
             version_o,
diff --git a/tests/test_http_parser.py b/tests/test_http_parser.py
index d76bb64bab5..ee7dc4aabc5 100644
--- a/tests/test_http_parser.py
+++ b/tests/test_http_parser.py
@@ -735,7 +735,7 @@ def test_max_header_value_size_continuation_under_limit(response) -> None:
     assert msg.version == (1, 1)
     assert msg.headers == CIMultiDict({"data": "test " + value.decode()})
     assert msg.raw_headers == ((b"data", b"test " + value),)
-    # assert not msg.should_close  # TODO: https://github.com/nodejs/llhttp/issues/354
+    assert msg.should_close
     assert msg.compression is None
     assert not msg.upgrade
     assert not msg.chunked