diff -pNaru5 perle-serial-3.9.2.orig-0002/pserial/perle-serial.c perle-serial-3.9.2/pserial/perle-serial.c
--- perle-serial-3.9.2.orig-0002/pserial/perle-serial.c	2021-09-14 11:10:48.772141908 -0400
+++ perle-serial-3.9.2/pserial/perle-serial.c	2021-09-14 11:10:59.679207370 -0400
@@ -70,10 +70,14 @@
  * SERIAL_PARANOIA_CHECK
  * 		Check the magic number for the async_structure where
  * 		ever possible.
  */
 
+#undef __KERNEL__
+#include <linux/tty_flags.h>
+#define __KERNEL__ 1
+
 #include <linux/version.h>
 #if ! defined (LINUX_VERSION_CODE)
 #error "Kernel version is not set"
 #endif