diff --git a/.github/workflows/changelog_check.yml b/.github/workflows/changelog_check.yml
index a8d592b1..a18212c9 100644
--- a/.github/workflows/changelog_check.yml
+++ b/.github/workflows/changelog_check.yml
@@ -12,6 +12,6 @@ jobs:
           ref: ${{github.event.pull_request.head.sha}}
       - uses: actions/setup-python@v4
         with:
-          python-version: "3.10"
+          python-version: "3.11"
       - run: python -m pip install towncrier
       - run: "scripts-dev/check_newsfragment.sh ${{ github.event.number }}"
diff --git a/.github/workflows/pipeline.yml b/.github/workflows/pipeline.yml
index 0bf75ee7..90e00ac5 100644
--- a/.github/workflows/pipeline.yml
+++ b/.github/workflows/pipeline.yml
@@ -37,7 +37,7 @@ jobs:
       - uses: actions/checkout@v3
       - uses: actions/setup-python@v4
         with:
-          python-version: "3.10"
+          python-version: "3.11"
       - run: python -m pip install -e .
       - run: python -m twisted.trial tests
 
diff --git a/changelog.d/373.misc b/changelog.d/373.misc
new file mode 100644
index 00000000..bfec9b82
--- /dev/null
+++ b/changelog.d/373.misc
@@ -0,0 +1 @@
+Update docker build and CI workflows to Python 3.11.
diff --git a/docker/Dockerfile b/docker/Dockerfile
index 0b37cc3f..38b5f578 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -9,7 +9,7 @@
 ###
 ### Stage 0: builder
 ###
-FROM python:3.10-slim as builder
+FROM python:3.11-slim as builder
 
 # Install git; Sygnal uses it to obtain the package version from the state of the
 # git repository.
@@ -25,7 +25,7 @@ RUN pip install --prefix="/install" --no-warn-script-location /sygnal
 ### Stage 1: runtime
 ###
 
-FROM python:3.10-slim
+FROM python:3.11-slim
 COPY --from=builder /install /usr/local
 
 EXPOSE 5000/tcp
diff --git a/tests/asyncio_test_helpers.py b/tests/asyncio_test_helpers.py
index 32dc7d94..6bd5dc91 100644
--- a/tests/asyncio_test_helpers.py
+++ b/tests/asyncio_test_helpers.py
@@ -1,7 +1,7 @@
 import logging
 import types
 from asyncio import AbstractEventLoop, transports
-from asyncio.protocols import BaseProtocol, Protocol
+from asyncio.protocols import BaseProtocol, BufferedProtocol, Protocol
 from asyncio.transports import Transport
 from contextvars import Context
 from typing import Any, Callable, List, Optional, Tuple
@@ -164,8 +164,13 @@ def abort(self) -> None:
 
     def pretend_to_receive(self, data: bytes) -> None:
         proto = self.get_protocol()
-        assert isinstance(proto, Protocol)
-        proto.data_received(data)
+        if isinstance(proto, Protocol):
+            proto.data_received(data)
+        elif isinstance(proto, BufferedProtocol):
+            data_len = len(data)
+            b = proto.get_buffer(data_len)
+            b[0:data_len] = data  # type: ignore[index]
+            proto.buffer_updated(data_len)
 
     def set_protocol(self, protocol: BaseProtocol) -> None:
         self.protocol = protocol