diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 80cbbbd..a34bb2b 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -31,6 +31,7 @@ jobs:
 
   test-python3:
     runs-on: ubuntu-24.04
+    container: ubuntu:focal
     strategy:
       matrix:
         python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"]