diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1c083708..cbac5ee3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -32,7 +32,7 @@ jobs:
             allow_failure: true
           - ruby: "truffleruby-head"
             allow_failure: true
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     continue-on-error: ${{ matrix.allow_failure }}
     env:
       BUNDLE_GEMFILE: ${{ matrix.gemfile }}