diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 407820dc..9cc04491 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -19,7 +19,7 @@ jobs:
         run: mypy --strict certifi
 
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       matrix:
         python-version: