diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 854c56a..3dd9855 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,6 +30,7 @@ jobs:
       - name: Govulncheck
         run: govulncheck ./...
         continue-on-error: true
+      - run: make commentcheck
       - run: go test -race -shuffle=on -cover -coverprofile=coverage.out ./...
       - run: go build ./...
       - run: make cover
diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 5d95071..d63c6cc 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -34,15 +34,15 @@ jobs:
       - name: Lint
         run: make lint
 
+      - name: Comment check
+        run: make commentcheck
+
       - name: Test (race)
         run: make test-race
 
       - name: Cover
         run: make cover
 
-      - name: Comment check
-        run: make commentcheck
-
       - name: Vulnerability check (non-blocking)
         continue-on-error: true
         run: |
diff --git a/Makefile b/Makefile
index 11d2cfc..21431e9 100644
--- a/Makefile
+++ b/Makefile
@@ -9,7 +9,7 @@ GO ?= go
 FMT_PKGS := $(shell $(GO) list $(PKG))
 FMT_DIRS := $(shell $(GO) list -f '{{.Dir}}' $(PKG))
 
-.PHONY: all init tidy fmt lint vet vuln test test-race cover cover-html build ci clean
+.PHONY: all init tidy fmt lint vet vuln commentcheck test test-race cover cover-html build ci clean
 
 all: build
 
@@ -25,11 +25,14 @@ fmt:
 	$(GO) run mvdan.cc/gofumpt@latest -w $(FMT_DIRS)
 
 lint:
-	$(GO) install github.com/golangci/golangci-lint/cmd/golangci-lint@latest
-	golangci-lint run --timeout=5m
+        $(GO) install github.com/golangci/golangci-lint/cmd/golangci-lint@latest
+        golangci-lint run --timeout=5m
+
+commentcheck:
+        $(GO) run ./cmd/commentcheck
 
 vet:
-	$(GO) vet $(PKG)
+        $(GO) vet $(PKG)
 
 test:
 	mkdir -p $(BUILD_DIR)
@@ -50,9 +53,9 @@ build:
 	$(GO) build -trimpath -buildvcs=false -ldflags="-s -w" -o $(BUILD_DIR)/$(APP) ./cmd/hclalign
 
 vuln:
-	$(GO) run golang.org/x/vuln/cmd/govulncheck@latest $(PKG)
+        $(GO) run golang.org/x/vuln/cmd/govulncheck@latest $(PKG)
 
-ci: tidy fmt lint vuln test cover build
+ci: tidy fmt lint vuln commentcheck test cover build
 
 clean:
 	rm -rf $(BUILD_DIR)
diff --git a/cmd/commentcheck/main.go b/cmd/commentcheck/main.go
new file mode 100644
index 0000000..9f84c22
--- /dev/null
+++ b/cmd/commentcheck/main.go
@@ -0,0 +1,62 @@
+// cmd/commentcheck/main.go
+package main
+
+import (
+	"fmt"
+	"go/parser"
+	"go/token"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func check(root string) error {
+	var bad []string
+	walk := func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() {
+			if d.Name() == "vendor" || strings.HasPrefix(d.Name(), ".") {
+				return filepath.SkipDir
+			}
+			return nil
+		}
+		if filepath.Ext(path) != ".go" {
+			return nil
+		}
+		fset := token.NewFileSet()
+		src, err := os.ReadFile(path)
+		if err != nil {
+			return err
+		}
+		file, err := parser.ParseFile(fset, path, src, parser.ParseComments)
+		if err != nil {
+			return err
+		}
+		for _, cg := range file.Comments {
+			for _, c := range cg.List {
+				if fset.Position(c.Slash).Line > 1 {
+					bad = append(bad, path)
+					return nil
+				}
+			}
+		}
+		return nil
+	}
+	if err := filepath.WalkDir(root, walk); err != nil {
+		return err
+	}
+	if len(bad) > 0 {
+		return fmt.Errorf("comments beyond first line: %s", strings.Join(bad, ", "))
+	}
+	return nil
+}
+
+func main() {
+	if err := check("."); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
diff --git a/cmd/commentcheck/main_test.go b/cmd/commentcheck/main_test.go
new file mode 100644
index 0000000..ef62e55
--- /dev/null
+++ b/cmd/commentcheck/main_test.go
@@ -0,0 +1,33 @@
+// cmd/commentcheck/main_test.go
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestCheck(t *testing.T) {
+	t.Run("compliant", func(t *testing.T) {
+		dir := t.TempDir()
+		write(t, dir, "ok.go", "// ok.go\npackage main\n")
+		if err := check(dir); err != nil {
+			t.Fatalf("unexpected error: %v", err)
+		}
+	})
+	t.Run("noncompliant", func(t *testing.T) {
+		dir := t.TempDir()
+		write(t, dir, "bad.go", "// bad.go\npackage main\n// bad\n")
+		if err := check(dir); err == nil {
+			t.Fatalf("expected error")
+		}
+	})
+}
+
+func write(t *testing.T, dir, name, content string) {
+	t.Helper()
+	path := filepath.Join(dir, name)
+	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
+		t.Fatalf("write %s: %v", name, err)
+	}
+}