diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3de23cb..5ea4b0a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -19,7 +19,7 @@ jobs:
           - "3.8"
           - "3.7"
           - "3.6"
-        os: [ubuntu-latest]
+        os: [ubuntu-20.04]
     runs-on: ${{ matrix.os }}
     name: "${{ matrix.os }} Python: ${{ matrix.python-version }}"
     steps: