diff --git a/firmware/hw_layer/ports/stm32/serial_over_usb/usbcfg.h b/firmware/hw_layer/ports/stm32/serial_over_usb/usbcfg.h
index ee3c4880cd..837af0efe0 100644
--- a/firmware/hw_layer/ports/stm32/serial_over_usb/usbcfg.h
+++ b/firmware/hw_layer/ports/stm32/serial_over_usb/usbcfg.h
@@ -21,7 +21,7 @@ extern const USBConfig usbcfg;
 extern SerialUSBConfig serusbcfg;
 extern SerialUSBDriver SDU1;
 
-void usbPopulateSerialNumber(const uint8_t* serialNumber, size_t bytes);
+EXTERNC void usbPopulateSerialNumber(const uint8_t* serialNumber, size_t bytes);
 
 #endif  /* USBCFG_H */