diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5ac8219..0b52074 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ['2.7', '3.0', '3.1', '3.2', '3.3', '3.4', 'head']
+        ruby: ['2.7', '3.0', '3.1', '3.2', '3.3', '3.4', '4.0', 'head']
     steps:
       - uses: actions/checkout@v4
       - name: Set up Ruby