diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 39c5531..66708e2 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -17,6 +17,11 @@ jobs:
             - name: Checkout repository
               uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
 
+            # Required for old theme build step.
+            - name: Checkout wporg CSS
+              run: |
+                svn export https://meta.svn.wordpress.org/sites/trunk/wordpress.org/public_html/wp-content/themes/pub/wporg/css themes/pub/wporg/css --quiet
+
             - name: Setup
               uses: WordPress/wporg-repo-tools/.github/actions/setup@trunk
               with: