diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index c0df6a2..01096b3 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -5,7 +5,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ 'ubuntu-16.04', 'ubuntu-18.04', 'macos-latest' ]
+        os: [ ubuntu-16.04, ubuntu-18.04, macos-latest ]
         ruby: [ 'ruby-2.4', '2.5', 'ruby-2.6.5', '2.7.0', 'truffleruby', 'jruby' ]
     runs-on: ${{ matrix.os }}
     steps:
diff --git a/README.md b/README.md
index 09fc4a2..74a1c70 100644
--- a/README.md
+++ b/README.md
@@ -40,7 +40,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ 'ubuntu-latest', 'macos-latest' ]
+        os: [ ubuntu-latest, macos-latest ]
         ruby: [ 'ruby-2.6', 'ruby-2.7', 'truffleruby-19.3.0', 'jruby-9.2.9.0' ]
     runs-on: ${{ matrix.os }}
     steps:
@@ -70,7 +70,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ 'ubuntu-latest', 'macos-latest' ]
+        os: [ ubuntu-latest, macos-latest ]
         ruby: [ '2.4', '2.5', '2.6', '2.7', 'truffleruby', 'jruby' ]
     runs-on: ${{ matrix.os }}
     steps: