diff --git a/.github/workflows/twisted_trunk.yml b/.github/workflows/twisted_trunk.yml
index 9c3d87abaf..de9318a885 100644
--- a/.github/workflows/twisted_trunk.yml
+++ b/.github/workflows/twisted_trunk.yml
@@ -135,12 +135,10 @@ jobs:
           poetry install --no-interaction --extras "all test"
         working-directory: /src
       - name: Run SyTest
+        # Bootstrap copies the patched pyproject.toml and poetry.lock, then installs
+        # with Poetry, layering Twisted trunk on top of the usual SyTest setup.
         run: /bootstrap.sh synapse
         working-directory: /src
-        env:
-          # Use offline mode to avoid reinstalling the pinned version of
-          # twisted.
-          OFFLINE: 1
       - name: Summarise results.tap
         if: ${{ always() }}
         run: /sytest/scripts/tap_to_gha.pl /logs/results.tap
diff --git a/changelog.d/20293.misc b/changelog.d/20293.misc
new file mode 100644
index 0000000000..ccf00ec409
--- /dev/null
+++ b/changelog.d/20293.misc
@@ -0,0 +1 @@
+Fix the `sytest` job failing on the Twisted trunk workflow due to missing build backend dependencies.
\ No newline at end of file