Index: linux/drivers/serial/8250.c
===================================================================
--- linux.orig/drivers/serial/8250.c	2006-02-13 16:49:48.000000000 +0100
+++ linux/drivers/serial/8250.c	2006-02-13 17:23:57.000000000 +0100
@@ -78,7 +78,9 @@
  * machine types want others as well - they're free
  * to redefine this in their header file.
  */
+#ifndef is_real_interrupt
 #define is_real_interrupt(irq)	((irq) != 0)
+#endif
 
 #ifdef CONFIG_SERIAL_8250_DETECT_IRQ
 #define CONFIG_SERIAL_DETECT_IRQ 1