diff --git a/libc/kernel/uapi/linux/can.h b/libc/kernel/uapi/linux/can.h
index 59fc31e..30eeca2 100644
--- a/libc/kernel/uapi/linux/can.h
+++ b/libc/kernel/uapi/linux/can.h
@@ -48,6 +48,7 @@
 };
 #define CANFD_BRS 0x01
 #define CANFD_ESI 0x02
+#define CANFD_FDF 0x04
 struct canfd_frame {
   canid_t can_id;
   __u8 len;