diff --git a/variants/m5stack_unit_c6l/platformio.ini b/variants/m5stack_unit_c6l/platformio.ini
index 190add0436..388532e0f1 100644
--- a/variants/m5stack_unit_c6l/platformio.ini
+++ b/variants/m5stack_unit_c6l/platformio.ini
@@ -109,5 +109,9 @@ lib_deps =
 
 [env:M5Stack_Unit_C6L_kiss_modem]
 extends = M5Stack_Unit_C6L
+build_flags = ${M5Stack_Unit_C6L.build_flags}
+  -D ARDUINO_USB_CDC_ON_BOOT=1
+  -D ARDUINO_USB_MODE=1
+  -D ENABLE_USB_INTERFACE
 build_src_filter = ${M5Stack_Unit_C6L.build_src_filter}
   +<../examples/kiss_modem/>