diff --git a/.github/workflows/latest_deps.yml b/.github/workflows/latest_deps.yml
index 7dac617c4..07229e56b 100644
--- a/.github/workflows/latest_deps.yml
+++ b/.github/workflows/latest_deps.yml
@@ -5,7 +5,7 @@
 #
 # As an overview this workflow:
 # - checks out develop,
-# - installs from source, pulling in the dependencies like a fresh `pip install` would, and 
+# - installs from source, pulling in the dependencies like a fresh `pip install` would, and
 # - runs mypy and test suites in that checkout.
 #
 # Based on the twisted trunk CI job.
@@ -26,12 +26,19 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+      - uses: Swatinem/rust-cache@v2
+
       # The dev dependencies aren't exposed in the wheel metadata (at least with current
       # poetry-core versions), so we install with poetry.
       - uses: matrix-org/setup-python-poetry@v1
         with:
           python-version: "3.x"
-          poetry-version: "1.2.0b1"
+          poetry-version: "1.2.0"
           extras: "all"
       # Dump installed versions for debugging.
       - run: poetry run pip list > before.txt
@@ -53,6 +60,14 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+      - uses: Swatinem/rust-cache@v2
+
       - run: sudo apt-get -qq install xmlsec1
       - name: Set up PostgreSQL ${{ matrix.postgres-version }}
         if: ${{ matrix.postgres-version }}
@@ -187,4 +202,3 @@ jobs:
         with:
           update_existing: true
           filename: .ci/latest_deps_build_failed_issue_template.md
-
diff --git a/.github/workflows/twisted_trunk.yml b/.github/workflows/twisted_trunk.yml
index 0906101cc..8fa2fbdea 100644
--- a/.github/workflows/twisted_trunk.yml
+++ b/.github/workflows/twisted_trunk.yml
@@ -16,6 +16,14 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+      - uses: Swatinem/rust-cache@v2
+
       - uses: matrix-org/setup-python-poetry@v1
         with:
           python-version: "3.x"
@@ -34,6 +42,14 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - run: sudo apt-get -qq install xmlsec1
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+      - uses: Swatinem/rust-cache@v2
+
       - uses: matrix-org/setup-python-poetry@v1
         with:
           python-version: "3.x"
@@ -66,6 +82,14 @@ jobs:
 
     steps:
       - uses: actions/checkout@v2
+
+      - name: Install Rust
+        uses: actions-rs/toolchain@v1
+        with:
+            toolchain: stable
+            override: true
+      - uses: Swatinem/rust-cache@v2
+
       - name: Patch dependencies
         # Note: The poetry commands want to create a virtualenv in /src/.venv/,
         #       but the sytest-synapse container expects it to be in /venv/.
diff --git a/changelog.d/13734.misc b/changelog.d/13734.misc
new file mode 100644
index 000000000..2e0dd68a0
--- /dev/null
+++ b/changelog.d/13734.misc
@@ -0,0 +1 @@
+Add a stub Rust crate.