diff --git a/.github/workflows/twisted_trunk.yml b/.github/workflows/twisted_trunk.yml
index f7a4ee7c13..67ccc03f6e 100644
--- a/.github/workflows/twisted_trunk.yml
+++ b/.github/workflows/twisted_trunk.yml
@@ -5,6 +5,9 @@ on:
     - cron: 0 8 * * *
 
   workflow_dispatch:
+    # NB: inputs are only present when this workflow is dispatched manually.
+    # (The default below is the default field value in the form to trigger
+    # a manual dispatch). Otherwise the inputs will evaluate to null.
     inputs:
       twisted_ref:
         description: Commit, branch or tag to checkout from upstream Twisted.
@@ -49,7 +52,7 @@ jobs:
           extras: "all"
       - run: |
           poetry remove twisted
-          poetry add --extras tls git+https://github.com/twisted/twisted.git#${{ inputs.twisted_ref }}
+          poetry add --extras tls git+https://github.com/twisted/twisted.git#${{ inputs.twisted_ref || 'trunk' }}
           poetry install --no-interaction --extras "all test"
       - name: Remove warn_unused_ignores from mypy config
         run: sed '/warn_unused_ignores = True/d' -i mypy.ini
diff --git a/changelog.d/16115.misc b/changelog.d/16115.misc
new file mode 100644
index 0000000000..f325d2a31d
--- /dev/null
+++ b/changelog.d/16115.misc
@@ -0,0 +1 @@
+Attempt to fix the twisted trunk job.
diff --git a/mypy.ini b/mypy.ini
index 1038b7d8c7..311a951aa8 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -45,6 +45,13 @@ warn_unused_ignores = False
 disallow_untyped_defs = False
 disallow_incomplete_defs = False
 
+[mypy-synapse.util.manhole]
+# This module imports something from Twisted which has a bad annotation in Twisted trunk,
+# but is unannotated in Twisted's latest release. We want to type-ignore the problem 
+# in the twisted trunk job, even though it has no effect on normal mypy runs.
+warn_unused_ignores = False
+
+
 ;; Dependencies without annotations
 ;; Before ignoring a module, check to see if type stubs are available.
 ;; The `typeshed` project maintains stubs here:
diff --git a/synapse/util/manhole.py b/synapse/util/manhole.py
index 48b8195ca1..8cb766860e 100644
--- a/synapse/util/manhole.py
+++ b/synapse/util/manhole.py
@@ -98,7 +98,9 @@ def manhole(settings: ManholeConfig, globals: Dict[str, Any]) -> ServerFactory:
         SynapseManhole, dict(globals, __name__="__console__")
     )
 
-    factory = manhole_ssh.ConchFactory(portal.Portal(rlm, [checker]))
+    # type-ignore: This is an error in Twisted's annotations. See
+    # https://github.com/twisted/twisted/issues/11812 and /11813 .
+    factory = manhole_ssh.ConchFactory(portal.Portal(rlm, [checker]))  # type: ignore[arg-type]
 
     # conch has the wrong type on these dicts (says bytes to bytes,
     # should be bytes to Keys judging by how it's used).