diff --git a/libraries/WiFi/src/WiFiUdp.cpp b/libraries/WiFi/src/WiFiUdp.cpp
index 22c3521d..121602a7 100644
--- a/libraries/WiFi/src/WiFiUdp.cpp
+++ b/libraries/WiFi/src/WiFiUdp.cpp
@@ -99,6 +99,7 @@ uint8_t WiFiUDP::beginMulticast(IPAddress a, uint16_t p){
 void WiFiUDP::stop(){
   if(tx_buffer){
     delete[] tx_buffer;
+    tx_buffer = NULL;
   }
   tx_buffer_len = 0;
   if(rx_buffer){