diff --git a/src/AsyncTCP.cpp b/src/AsyncTCP.cpp
index d112672..76282d6 100644
--- a/src/AsyncTCP.cpp
+++ b/src/AsyncTCP.cpp
@@ -447,7 +447,7 @@ static esp_err_t _tcp_write(tcp_pcb * pcb, int8_t closed_slot, const char* data,
 static err_t _tcp_recved_api(struct tcpip_api_call_data *api_call_msg){
     tcp_api_call_t * msg = (tcp_api_call_t *)api_call_msg;
     msg->err = ERR_CONN;
-    if(msg->closed_slot != INVALID_CLOSED_SLOT && !_closed_slots[msg->closed_slot]) {
+    if(msg->closed_slot == INVALID_CLOSED_SLOT || !_closed_slots[msg->closed_slot]) {
         msg->err = 0;
         tcp_recved(msg->pcb, msg->received);
     }