diff --git a/src/core/tcp.c b/src/core/tcp.c
index 63e44457..75be86bb 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -684,6 +684,7 @@ tcp_listen_with_backlog_and_err(struct tcp_pcb *pcb, u8_t backlog, err_t *err)
       if ((lpcb->local_port == pcb->local_port) &&
           ip_addr_cmp(&lpcb->local_ip, &pcb->local_ip)) {
         /* this address/port is already used */
+        lpcb = NULL;
         res = ERR_USE;
         goto done;
       }