diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 30231244593..961fe690c4d 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -104,6 +104,15 @@ jobs:
       - uses: actions/checkout@v2
         with:
           fetch-depth: 2
+      # TODO: Remove this step when the compatibility issue between mozjs and
+      #       Homebrew's Python 3.10 formula (servo/rust-mozjs#559) is fixed
+      - name: Select Python 3.9
+        run: |
+          brew install python@3.9
+          cd $(dirname $(which python3.9))
+          rm -f python3 pip3
+          ln -s python3.9 python3
+          ln -s pip3.9 pip3
       - name: Bootstrap
         run: |
           python3 -m pip install --upgrade pip virtualenv
diff --git a/.github/workflows/nightly.yml b/.github/workflows/nightly.yml
index 4a505c4db54..5afe7a079b2 100644
--- a/.github/workflows/nightly.yml
+++ b/.github/workflows/nightly.yml
@@ -39,6 +39,15 @@ jobs:
       - uses: actions/checkout@v2
         with:
           fetch-depth: 2
+      # TODO: Remove this step when the compatibility issue between mozjs and
+      #       Homebrew's Python 3.10 formula (servo/rust-mozjs#559) is fixed
+      - name: Select Python 3.9
+        run: |
+          brew install python@3.9
+          cd $(dirname $(which python3.9))
+          rm -f python3 pip3
+          ln -s python3.9 python3
+          ln -s pip3.9 pip3
       - name: Bootstrap
         run: |
           python3 -m pip install --upgrade pip virtualenv