diff --git a/cores/esp8266/HardwareSerial.cpp b/cores/esp8266/HardwareSerial.cpp
index fb9019a2c..18a581dde 100644
--- a/cores/esp8266/HardwareSerial.cpp
+++ b/cores/esp8266/HardwareSerial.cpp
@@ -56,6 +56,7 @@ void HardwareSerial::end()
     }
 
     uart_uninit(_uart);
+    _uart = NULL;
 }
 
 void HardwareSerial::swap(uint8_t tx_pin)