diff --git a/cores/esp32/USB.cpp b/cores/esp32/USB.cpp
index 6133212f..d2b67f6b 100644
--- a/cores/esp32/USB.cpp
+++ b/cores/esp32/USB.cpp
@@ -29,7 +29,7 @@
 #define USB_PRODUCT ARDUINO_BOARD
 #endif
 #ifndef USB_SERIAL
-#define USB_SERIAL ""
+#define USB_SERIAL "0"
 #endif
 
 extern "C" {