diff --git a/cores/arduino/HardwareSerial.cpp b/cores/arduino/HardwareSerial.cpp
index 4dd8fd02a4..0ad990c466 100644
--- a/cores/arduino/HardwareSerial.cpp
+++ b/cores/arduino/HardwareSerial.cpp
@@ -449,10 +449,14 @@ void HardwareSerial::begin(unsigned long baud, byte config)
   uart_init(&_serial, (uint32_t)baud, databits, parity, stopbits, _rx_invert, _tx_invert, _data_invert);
   enableHalfDuplexRx();
   uart_attach_rx_callback(&_serial, _rx_complete_irq);
+
+  _ready = true;
 }
 
 void HardwareSerial::end()
 {
+  _ready = false;
+
   // wait for transmission of outgoing data
   flush(TX_TIMEOUT);
 
diff --git a/cores/arduino/HardwareSerial.h b/cores/arduino/HardwareSerial.h
index 3ed29a873d..be670e9540 100644
--- a/cores/arduino/HardwareSerial.h
+++ b/cores/arduino/HardwareSerial.h
@@ -146,7 +146,7 @@ class HardwareSerial : public Stream {
     using Print::write; // pull in write(str) from Print
     operator bool()
     {
-      return true;
+      return _ready;
     }
 
     void setRx(uint32_t _rx);
@@ -189,6 +189,7 @@ class HardwareSerial : public Stream {
 #endif // HAL_UART_MODULE_ENABLED && !HAL_UART_MODULE_ONLY
 
   private:
+    bool _ready;
     bool _rx_enabled;
     uint8_t _config;
     unsigned long _baud;