diff --git a/src/cmd/cos_gpu_installer/main.go b/src/cmd/cos_gpu_installer/main.go
index 2414ae7..d3a6b24 100644
--- a/src/cmd/cos_gpu_installer/main.go
+++ b/src/cmd/cos_gpu_installer/main.go
@@ -19,7 +19,8 @@
 	flag.Parse()
 
 	log.V(2).Info("Checking if this is the only cos_gpu_installer that is running.")
-	utils.Flock()
+	f := utils.Flock()
+	defer f.Close()
 
 	subcommands.Register(subcommands.HelpCommand(), "")
 	subcommands.Register(subcommands.FlagsCommand(), "")
diff --git a/src/pkg/utils/utils.go b/src/pkg/utils/utils.go
index 7bc9126..0d8094a 100644
--- a/src/pkg/utils/utils.go
+++ b/src/pkg/utils/utils.go
@@ -70,7 +70,7 @@
 }
 
 // Flock exclusively locks a special file on the host to make sure only one calling process is running at any time.
-func Flock() {
+func Flock() *os.File {
 	// TODO(mikewu): generalize Flock to make it useful for other use cases.
 	f, err := os.OpenFile(lockFile, os.O_RDONLY|os.O_CREATE, 0666)
 	if err != nil {
@@ -79,6 +79,7 @@
 	if err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil {
 		glog.Exitf("File %s is locked. Other process might be running.", lockFile)
 	}
+	return f
 }
 
 // DownloadContentFromURL downloads file from a given URL.