diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index a864d51..9101a3c 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -6,7 +6,7 @@ on:
 
 jobs:
   build:
-    runs-on: ubuntu-latest
+    runs-on: '${{ matrix.os }}'
     # https://wildwolf.name/github-actions-how-to-avoid-running-the-same-workflow-multiple-times/
     if: >
       github.event_name != 'pull_request'
@@ -15,17 +15,25 @@ jobs:
       matrix:
         # Not all Python versions are available for linux AND x64
         # https://raw.githubusercontent.com/actions/python-versions/main/versions-manifest.json
-        python-version: [3.5, 3.6, 3.7, 3.8, 3.9, '3.10', '3.11.0-beta - 3.11', 'pypy-3.7', 'pypy-3.8', 'pypy-3.9']
+        os: ['ubuntu-latest']
+        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', 'pypy-3.7', 'pypy-3.8', 'pypy-3.9']
         extra: ['', '-smtp']
         # The forced pytest versions correspond with the lower bounds in tox.ini
         pytest-version: ['', '--force-dep pytest==4', '--force-dep pytest==6.2.4']
+        include:
+        - os: 'ubuntu-20.04'
+          python-version: '3.5'
+          pytest-version: ''
+        - os: 'ubuntu-20.04'
+          python-version: '3.5'
+          pytest-version: '--force-dep pytest==4'
+        - os: 'ubuntu-20.04'
+          python-version: '3.6'
         exclude:
-          - python-version: '3.5'
-            pytest-version: '--force-dep pytest==6.2.4'
-          - python-version: '3.10'
-            pytest-version: '--force-dep pytest==4'
-          - python-version: '3.11.0-beta - 3.11'
-            pytest-version: '--force-dep pytest==4'
+        - python-version: '3.10'
+          pytest-version: '--force-dep pytest==4'
+        - python-version: '3.11'
+          pytest-version: '--force-dep pytest==4'
       fail-fast: false
 
     steps: