diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5494127..b629e35 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -4,7 +4,7 @@ on: [push, pull_request]
 
 jobs:
     lint:
-        runs-on: ubuntu-latest
+        runs-on: ubuntu-22.04
         steps:
             - uses: actions/checkout@v4
             - name: Set up Python
@@ -20,7 +20,7 @@ jobs:
                   make lint
 
     test:
-        runs-on: ubuntu-latest
+        runs-on: ubuntu-22.04
         strategy:
             matrix:
                 python-version: ["3.10", "3.11", "3.12"]
@@ -40,7 +40,7 @@ jobs:
                   make test
 
     publish:
-        runs-on: ubuntu-latest
+        runs-on: ubuntu-22.04
         needs: [lint, test]
         if: startsWith(github.ref, 'refs/tags')
         steps:
diff --git a/server/app.yaml b/server/app.yaml
index 828b649..26347f5 100644
--- a/server/app.yaml
+++ b/server/app.yaml
@@ -1,4 +1,4 @@
-runtime: python311
+runtime: python312  # Make sure github test runners use same image and python versions.
 
 handlers:
   - url: /static