diff --git a/cores/arduino/CDC.cpp b/cores/arduino/CDC.cpp
index 7206aa6..1275304 100644
--- a/cores/arduino/CDC.cpp
+++ b/cores/arduino/CDC.cpp
@@ -213,6 +213,12 @@ size_t Serial_::write(uint8_t c)
 	return 0;
 }
 
+Serial_::operator bool() {
+	if (_usbLineInfo.lineState > 0)
+		return true;
+	return false;
+}
+
 Serial_ Serial;
 
 #endif
diff --git a/cores/arduino/HardwareSerial.cpp b/cores/arduino/HardwareSerial.cpp
index 9985b78..f40ddee 100644
--- a/cores/arduino/HardwareSerial.cpp
+++ b/cores/arduino/HardwareSerial.cpp
@@ -398,6 +398,10 @@ size_t HardwareSerial::write(uint8_t c)
   return 1;
 }
 
+HardwareSerial::operator bool() {
+	return true;
+}
+
 // Preinstantiate Objects //////////////////////////////////////////////////////
 
 #if defined(UBRRH) && defined(UBRRL)
diff --git a/cores/arduino/HardwareSerial.h b/cores/arduino/HardwareSerial.h
index 176abe1..bf4924c 100644
--- a/cores/arduino/HardwareSerial.h
+++ b/cores/arduino/HardwareSerial.h
@@ -57,6 +57,7 @@ class HardwareSerial : public Stream
     virtual void flush(void);
     virtual size_t write(uint8_t);
     using Print::write; // pull in write(str) and write(buf, size) from Print
+    operator bool();
 };
 
 #if defined(UBRRH) || defined(UBRR0H)
diff --git a/cores/arduino/USBAPI.h b/cores/arduino/USBAPI.h
index 5169e65..f66cb16 100644
--- a/cores/arduino/USBAPI.h
+++ b/cores/arduino/USBAPI.h
@@ -39,6 +39,7 @@ public:
 	virtual int read(void);
 	virtual void flush(void);
 	virtual size_t write(uint8_t);
+	operator bool();
 };
 extern Serial_ Serial;