diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 24b58f8..d5674eb 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -11,7 +11,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ ubuntu-latest, macos-latest ]
+        os: [ ubuntu-20.04, macos-latest ]
         python-version: [ 2.7, 3.8, 3.9 ]
     steps:
       - uses: actions/checkout@v2