diff --git a/tests/requests/invalid/rfc9110_trailer_forbidden_cl_01.http b/tests/requests/invalid/rfc9110_trailer_forbidden_cl_01.http
new file mode 100644
index 00000000..7562e1a8
--- /dev/null
+++ b/tests/requests/invalid/rfc9110_trailer_forbidden_cl_01.http
@@ -0,0 +1,9 @@
+POST /p HTTP/1.1\r\n
+Host: example.com\r\n
+Transfer-Encoding: chunked\r\n
+\r\n
+5\r\n
+hello\r\n
+0\r\n
+Content-Length: 99\r\n
+\r\n
diff --git a/tests/requests/invalid/rfc9110_trailer_forbidden_cl_01.py b/tests/requests/invalid/rfc9110_trailer_forbidden_cl_01.py
new file mode 100644
index 00000000..b0f8ccae
--- /dev/null
+++ b/tests/requests/invalid/rfc9110_trailer_forbidden_cl_01.py
@@ -0,0 +1,9 @@
+#
+# This file is part of gunicorn released under the MIT license.
+# See the NOTICE for more information.
+
+# RFC 9110 section 6.5.1: Content-Length in trailers is a classic
+# smuggling vector; origin must reject.
+from gunicorn.http.errors import InvalidHeaderName
+request = InvalidHeaderName
+python_only = True
diff --git a/tests/requests/invalid/rfc9110_trailer_forbidden_host_01.http b/tests/requests/invalid/rfc9110_trailer_forbidden_host_01.http
new file mode 100644
index 00000000..348082e7
--- /dev/null
+++ b/tests/requests/invalid/rfc9110_trailer_forbidden_host_01.http
@@ -0,0 +1,9 @@
+POST /p HTTP/1.1\r\n
+Host: example.com\r\n
+Transfer-Encoding: chunked\r\n
+\r\n
+5\r\n
+hello\r\n
+0\r\n
+Host: evil.example.com\r\n
+\r\n
diff --git a/tests/requests/invalid/rfc9110_trailer_forbidden_host_01.py b/tests/requests/invalid/rfc9110_trailer_forbidden_host_01.py
new file mode 100644
index 00000000..fe897329
--- /dev/null
+++ b/tests/requests/invalid/rfc9110_trailer_forbidden_host_01.py
@@ -0,0 +1,11 @@
+#
+# This file is part of gunicorn released under the MIT license.
+# See the NOTICE for more information.
+
+# RFC 9110 section 6.5.1: certain header fields must not be sent in
+# trailers because they alter routing or message framing (e.g. Host,
+# Content-Length, Transfer-Encoding). Accepting them enables smuggling.
+from gunicorn.http.errors import InvalidHeaderName
+request = InvalidHeaderName
+# The C parser (gunicorn_h1c) does not yet enforce this rule.
+python_only = True
diff --git a/tests/requests/invalid/rfc9110_trailer_forbidden_te_01.http b/tests/requests/invalid/rfc9110_trailer_forbidden_te_01.http
new file mode 100644
index 00000000..e5c98d16
--- /dev/null
+++ b/tests/requests/invalid/rfc9110_trailer_forbidden_te_01.http
@@ -0,0 +1,9 @@
+POST /p HTTP/1.1\r\n
+Host: example.com\r\n
+Transfer-Encoding: chunked\r\n
+\r\n
+5\r\n
+hello\r\n
+0\r\n
+Transfer-Encoding: chunked\r\n
+\r\n
diff --git a/tests/requests/invalid/rfc9110_trailer_forbidden_te_01.py b/tests/requests/invalid/rfc9110_trailer_forbidden_te_01.py
new file mode 100644
index 00000000..caa2f5ac
--- /dev/null
+++ b/tests/requests/invalid/rfc9110_trailer_forbidden_te_01.py
@@ -0,0 +1,9 @@
+#
+# This file is part of gunicorn released under the MIT license.
+# See the NOTICE for more information.
+
+# RFC 9110 section 6.5.1: Transfer-Encoding in trailers alters framing
+# and must not be accepted.
+from gunicorn.http.errors import InvalidHeaderName
+request = InvalidHeaderName
+python_only = True