diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index d7f0e76..8876c31 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -9,7 +9,7 @@ on:
 jobs:
   test:
 
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     strategy:
       fail-fast: false