diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 08e45f93..ebd77fbc 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-16.04, ubuntu-18.04, macos-latest ]
+        os: [ ubuntu-16.04, ubuntu-18.04, ubuntu-20.04, macos-latest ]
         ruby: [ "truffleruby-20.1.0" ]
     runs-on: ${{ matrix.os }}
     steps: