diff --git a/src/device/usbd_pvt.h b/src/device/usbd_pvt.h
index e430a81d9..a5d223329 100644
--- a/src/device/usbd_pvt.h
+++ b/src/device/usbd_pvt.h
@@ -54,6 +54,7 @@ typedef struct
 
 // Invoked when initializing device stack to get additional class drivers.
 // Can optionally implemented by application to extend/overwrite class driver support.
+// Note: The drivers array must be accessible at all time when stack is active
 usbd_class_driver_t const* usbd_app_driver_get_cb(uint8_t* driver_count) TU_ATTR_WEAK;
 
 //--------------------------------------------------------------------+