diff --git a/src/api.rs b/src/api.rs
index 003121b..04e08cb 100644
--- a/src/api.rs
+++ b/src/api.rs
@@ -7,16 +7,15 @@ use tokio_util::sync::CancellationToken;
 static TUN_QUIT: Mutex<Option<CancellationToken>> = Mutex::new(None);
 
 pub(crate) fn tun2proxy_internal_run(args: Args, tun_mtu: u16) -> c_int {
-    let mut lock = TUN_QUIT.lock().unwrap();
-    if lock.is_some() {
-        log::error!("tun2proxy already started");
-        return -1;
-    }
-
     let shutdown_token = CancellationToken::new();
-    *lock = Some(shutdown_token.clone());
-    // explicit drop to avoid holding mutex lock while running proxy.
-    drop(lock);
+    {
+        let mut lock = TUN_QUIT.lock().unwrap();
+        if lock.is_some() {
+            log::error!("tun2proxy already started");
+            return -1;
+        }
+        *lock = Some(shutdown_token.clone());
+    }
 
     let block = async move {
         log::info!("Proxy {} server: {}", args.proxy.proxy_type, args.proxy.addr);