diff --git a/main_test.go b/main_test.go
index 7849aa98d..8b5c168dc 100644
--- a/main_test.go
+++ b/main_test.go
@@ -136,12 +136,6 @@ func TestCreateAndRemovePidFile(t *testing.T) {
 		t.Errorf("pid file should be created but, %s", err)
 	}
 
-	if runtime.GOOS != "windows" {
-		if err := pidfile.Create(fpath); err == nil || !strings.HasPrefix(err.Error(), "pidfile found, try stopping another running mackerel-agent or delete") {
-			t.Errorf("creating pid file should be failed when the running process exists, %s", err)
-		}
-	}
-
 	pidfile.Remove(fpath)
 	if err := pidfile.Create(fpath); err != nil {
 		t.Errorf("pid file should be created but, %s", err)
diff --git a/pidfile/pidfile_test.go b/pidfile/pidfile_test.go
index 91953c8ab..660e27b47 100644
--- a/pidfile/pidfile_test.go
+++ b/pidfile/pidfile_test.go
@@ -3,6 +3,7 @@
 package pidfile
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -31,7 +32,16 @@ func TestCreate(t *testing.T) {
 	if pid != os.Getpid() {
 		t.Errorf("contents of pidfile does not match pid. content: %d, pid: %d", pid, os.Getpid())
 	}
+}
 
+func TestCreate_mutex(t *testing.T) {
+	dir, err := ioutil.TempDir("", "")
+	if err != nil {
+		t.Fatalf("failed to create tempdir")
+	}
+	defer os.RemoveAll(dir)
+	pidfile := filepath.Join(dir, "pidfile")
+	ioutil.WriteFile(pidfile, []byte(fmt.Sprintf("%d", os.Getppid())), 0644)
 	err = Create(pidfile)
 	if err == nil {
 		t.Errorf("Successfully overwriting the pidfile unintentionally")