diff --git a/src/AsyncTCP.cpp b/src/AsyncTCP.cpp
index 1a4e8bd..e048d58 100644
--- a/src/AsyncTCP.cpp
+++ b/src/AsyncTCP.cpp
@@ -581,7 +581,7 @@ AsyncClient::AsyncClient(tcp_pcb* pcb)
 , _tx_last_packet(0)
 , _rx_timeout(0)
 , _rx_last_ack(0)
-, _ack_timeout(ASYNC_MAX_ACK_TIME)
+, _ack_timeout(CONFIG_ASYNC_TCP_MAX_ACK_TIME)
 , _connect_port(0)
 , prev(NULL)
 , next(NULL)
diff --git a/src/AsyncTCP.h b/src/AsyncTCP.h
index b79afc0..7486f5e 100644
--- a/src/AsyncTCP.h
+++ b/src/AsyncTCP.h
@@ -69,9 +69,12 @@ extern "C" {
 #define CONFIG_ASYNC_TCP_QUEUE_SIZE 64
 #endif
 
+#ifndef CONFIG_ASYNC_TCP_MAX_ACK_TIME
+#define CONFIG_ASYNC_TCP_MAX_ACK_TIME 5000
+#endif
+
 class AsyncClient;
 
-#define ASYNC_MAX_ACK_TIME 5000
 #define ASYNC_WRITE_FLAG_COPY 0x01 //will allocate new buffer to hold the data while sending (else will hold reference to the data given)
 #define ASYNC_WRITE_FLAG_MORE 0x02 //will not send PSH flag, meaning that there should be more data to be sent before the application should react.