diff --git a/CHANGES/9018.bugfix.rst b/CHANGES/9018.bugfix.rst
new file mode 100644
index 00000000000..2de6d142900
--- /dev/null
+++ b/CHANGES/9018.bugfix.rst
@@ -0,0 +1 @@
+Updated Python parser to reject messages after a close message, matching C parser behaviour -- by :user:`Dreamsorcerer`.
diff --git a/aiohttp/http_parser.py b/aiohttp/http_parser.py
index a79710414af..024e53f4d40 100644
--- a/aiohttp/http_parser.py
+++ b/aiohttp/http_parser.py
@@ -306,6 +306,7 @@ def feed_data(
         start_pos = 0
         loop = self.loop
 
+        should_close = False
         while start_pos < data_len:
             # read HTTP message (request/response line + headers), \r\n\r\n
             # and split by lines
@@ -317,6 +318,9 @@ def feed_data(
                     continue
 
                 if pos >= start_pos:
+                    if should_close:
+                        raise BadHttpMessage("Data after `Connection: close`")
+
                     # line found
                     line = data[start_pos:pos]
                     if SEP == b"\n":  # For lax response parsing
@@ -426,6 +430,7 @@ def get_content_length() -> Optional[int]:
                             payload = EMPTY_PAYLOAD
 
                         messages.append((msg, payload))
+                        should_close = msg.should_close
                 else:
                     self._tail = data[start_pos:]
                     data = EMPTY
diff --git a/tests/test_http_parser.py b/tests/test_http_parser.py
index 23ad9bf7758..96a3f11d1cf 100644
--- a/tests/test_http_parser.py
+++ b/tests/test_http_parser.py
@@ -851,6 +851,14 @@ def test_http_request_bad_status_line_whitespace(parser: HttpRequestParser) -> N
         parser.feed_data(text)
 
 
+def test_http_request_message_after_close(parser: HttpRequestParser) -> None:
+    text = b"GET / HTTP/1.1\r\nConnection: close\r\n\r\nInvalid\r\n\r\n"
+    with pytest.raises(
+        http_exceptions.BadHttpMessage, match="Data after `Connection: close`"
+    ):
+        parser.feed_data(text)
+
+
 def test_http_request_upgrade(parser: HttpRequestParser) -> None:
     text = (
         b"GET /test HTTP/1.1\r\n"