diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6ec90bdf..b8dc103f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -9,7 +9,7 @@ jobs:
       Django ${{ matrix.django-version }},
       Redis.py ${{ matrix.redis-version }}
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     strategy:
       fail-fast: false
@@ -86,7 +86,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          python -m pip install --upgrade tox tox-gh-actions
+          python -m pip install --upgrade "tox<4" tox-gh-actions
 
       - name: Tox tests
         run: |
@@ -149,7 +149,7 @@ jobs:
       - name: Install dependencies
         run: |
           python -m pip install --upgrade pip
-          python -m pip install --upgrade tox
+          python -m pip install --upgrade "tox<4"
 
       - name: Run ${{ matrix.tool }}
         run: tox -e ${{ matrix.tool }}
diff --git a/changelog.d/645.misc b/changelog.d/645.misc
new file mode 100644
index 00000000..318edf46
--- /dev/null
+++ b/changelog.d/645.misc
@@ -0,0 +1 @@
+Fix CI, running tox<4 to still support Python 3.6.
\ No newline at end of file