diff --git a/ext/lwip/src/core/tcp.c b/ext/lwip/src/core/tcp.c
index e9a2113..697bc2d 100755
--- a/ext/lwip/src/core/tcp.c
+++ b/ext/lwip/src/core/tcp.c
@@ -996,7 +996,7 @@ tcp_slowtmr_start:
   prev = NULL;
   pcb = tcp_active_pcbs;
   if (pcb == NULL) {
-    LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: no active pcbs\n"));
+    LWIP_DEBUGF(TCP_DEBUG_TMR, ("tcp_slowtmr: no active pcbs\n"));
   }
   while (pcb != NULL) {
     LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: processing active pcb\n"));
diff --git a/include/lwipopts.h b/include/lwipopts.h
index d122af9..bc97ac1 100644
--- a/include/lwipopts.h
+++ b/include/lwipopts.h
@@ -100,6 +100,7 @@
 #define SYS_DEBUG                       LWIP_DBG_OFF
 #define TIMERS_DEBUG                    LWIP_DBG_OFF
 // TCP
+#define TCP_DEBUG_TMR					LWIP_DBG_OFF // not standard in lwIP, added for debugging convenience
 #define TCP_DEBUG                       LWIP_DBG_OFF
 #define TCP_INPUT_DEBUG                 LWIP_DBG_OFF
 #define TCP_FR_DEBUG                    LWIP_DBG_OFF