diff --git a/system/usbhcd.c b/system/usbhcd.c
index fdae1d3..cb50b1b 100644
--- a/system/usbhcd.c
+++ b/system/usbhcd.c
@@ -679,7 +679,7 @@ bool find_attached_usb_keyboards(const usb_hcd_t *hcd, const usb_hub_t *hub, int
     return keyboard_found;
 }
 
-bool process_usb_keyboard_report(const usb_hcd_t *hcd, hid_kbd_rpt_t *report, hid_kbd_rpt_t *prev_report)
+bool process_usb_keyboard_report(const usb_hcd_t *hcd, const hid_kbd_rpt_t *report, const hid_kbd_rpt_t *prev_report)
 {
     hcd_workspace_t *ws = hcd->ws;
 
diff --git a/system/usbhcd.h b/system/usbhcd.h
index 1e98958..3d1fc29 100644
--- a/system/usbhcd.h
+++ b/system/usbhcd.h
@@ -274,7 +274,7 @@ bool find_attached_usb_keyboards(const usb_hcd_t *hcd, const usb_hub_t *hub, int
  *
  * Used internally by the various HCI drivers.
  */
-bool process_usb_keyboard_report(const usb_hcd_t *hcd, hid_kbd_rpt_t *report, hid_kbd_rpt_t *prev_report);
+bool process_usb_keyboard_report(const usb_hcd_t *hcd, const hid_kbd_rpt_t *report, const hid_kbd_rpt_t *prev_report);
 
 /**
  * Scans the attached USB devices and initialises all HID keyboard devices