diff --git a/src/proxy/tcp_proxy_server.c b/src/proxy/tcp_proxy_server.c
index 4fc237eb..0fb5c954 100644
--- a/src/proxy/tcp_proxy_server.c
+++ b/src/proxy/tcp_proxy_server.c
@@ -156,6 +156,7 @@ static void on_error_cb(struct tcp_conn* tc, int err, void* arg) {
 
 static void diag_timer_cb(void* arg) {
     struct tcp_proxy_server_conn* rc = (struct tcp_proxy_server_conn*)arg;
+    rc->diag_timer = NULL;
     struct tcp_conn* tc = rc->tc;
     if (!tc || tc->sock == SOCKET_INVALID) return;