diff --git a/.github/workflows/run-tests.yml b/.github/workflows/run-tests.yml
index cf0be256..cad9ff67 100644
--- a/.github/workflows/run-tests.yml
+++ b/.github/workflows/run-tests.yml
@@ -18,9 +18,13 @@ jobs:
     if: "! contains(toJSON(github.event.commits.*.message), '[skip ci]')"
     strategy:
       matrix:
-        python-version: ['3.8', '3.10', '3.11']
+        python-version: ['3.8', '3.9', '3.10', '3.11']
         platform: [ubuntu-latest, macos-latest, windows-latest]
         exclude: # Only test on the oldest and latest supported stable Python on macOS and Windows.
+          - platform: macos-latest
+            python-version: 3.9
+          - platform: windows-latest
+            python-version: 3.9
           - platform: macos-latest
             python-version: 3.10
           - platform: windows-latest