diff --git a/.github/workflows/pytest.yml b/.github/workflows/pytest.yml
index 1e6f56e..dc88a54 100644
--- a/.github/workflows/pytest.yml
+++ b/.github/workflows/pytest.yml
@@ -4,7 +4,7 @@ on: [push, pull_request]
 
 jobs:
   pytest:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     strategy:
       matrix: