diff --git a/firmware/usbstack/usb_serial.c b/firmware/usbstack/usb_serial.c
index 99b8bb2c3f..d36151afd1 100644
--- a/firmware/usbstack/usb_serial.c
+++ b/firmware/usbstack/usb_serial.c
@@ -169,7 +169,7 @@ static void sendout(void)
     }
 }
 
-void usb_serial_send(unsigned char *data,int length)
+void usb_serial_send(const unsigned char *data,int length)
 {
     int freestart, available_end_space, i;
 
diff --git a/firmware/usbstack/usb_serial.h b/firmware/usbstack/usb_serial.h
index 2701a96cd3..f1a603c4a3 100644
--- a/firmware/usbstack/usb_serial.h
+++ b/firmware/usbstack/usb_serial.h
@@ -32,7 +32,7 @@ void usb_serial_disconnect(void);
 void usb_serial_transfer_complete(int ep,int dir, int status, int length);
 bool usb_serial_control_request(struct usb_ctrlrequest* req, unsigned char *dest);
 
-void usb_serial_send(unsigned char *data,int length);
+void usb_serial_send(const unsigned char *data, int length);
 
 #endif