diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 367373a..1cbef43 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -11,11 +11,16 @@ permissions:
 jobs:
   rspec:
     name: RSpec (ruby ${{ matrix.ruby-version }})
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:
         ruby-version:
+          - '2.0'
+          - '2.1'
+          - '2.2'
+          - '2.3'
+          - '2.4'
           - '2.5'
           - '2.6'
           - '2.7'