diff --git a/cores/arduino/Serial.cpp b/cores/arduino/Serial.cpp
index 615f3b8ec..2e55fbf32 100644
--- a/cores/arduino/Serial.cpp
+++ b/cores/arduino/Serial.cpp
@@ -125,7 +125,7 @@ size_t UART::write(const uint8_t* c, size_t len) {
 	while (!_serial->writeable()) {}
 	_serial->set_blocking(true);
 	int ret = _serial->write(c, len);
-	return ret == -1 ? 0 : 1;
+	return ret == -1 ? 0 : len;
 }
 
 void UART::block_tx(int _a) {