diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 6cd5604..473a11f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -6,8 +6,8 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
-    - uses: actions/setup-go@v4
-      with:
-        go-version: '1.20'
-    - run: go test -v -cover ./...
+      - uses: actions/checkout@v3
+      - uses: actions/setup-go@v4
+        with:
+          go-version: "1.21.5"
+      - run: go test -v -cover ./...
diff --git a/go.mod b/go.mod
index 51a4626..166b271 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module gmachine
 
-go 1.20
+go 1.21.5
 
 require (
 	github.com/google/go-cmp v0.5.9