diff --git a/.github/workflows/test-ci.yml b/.github/workflows/test-ci.yml
index 0b9ef72c..bf53b406 100644
--- a/.github/workflows/test-ci.yml
+++ b/.github/workflows/test-ci.yml
@@ -13,7 +13,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        # ubuntu-20.04 is the last version that supports python 3.6
+        os: [ubuntu-20.04, macos-latest, windows-latest]
         python-version: ['3.6', '3.7', '3.8', '3.9', '3.10']
     runs-on: ${{ matrix.os }}